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Hanlon's Razor

Never attribute to malice that which is adequately explained by stupidity.


Hanlon's razor asks for reflection in situations where we perceive behavior to be intentionally malicious. A useful exercise is to rethink the scenario by replacing the malicious intent with reasons such as stupidity, stress or just plain old misunderstanding.


  • Your five-year old probably isn't making a mess to make your life miserable but rather because they're a toddler.

  • A social networking website probably didn't flag your content out of malice but rather due to a faulty algorithm.

Occam's Razor

When comparing hypotheses, the one with the fewest assumptions should be selected.


Occam's razor originally stated that entities should not be multiplied unnecessarily. In other words, don't complicate things when you don't need to. By shaving off unnecessary additions, the resulting explanation tends to be less ambiguous, easier to verify, and just plain simpler. Occam's Razor is often mentioned when selecting a simple solution over a complex one. Note that this is a slightly stronger form than the principle intended--reality can be complex and there are cases where the simple solution is not correct.


  • A sore throat during during the winter is probably the result of a cold even though the symptoms match a rare terminal disease on WebMD.

  • The pyramids being built by humans has far less assumptions than the pyramids being built by aliens.

First Principles Reasoning

Break complex problems into foundational elements and use these elements to build your reasoning.


A first principle is a foundational assumption or proposition that cannot be derived from other assumption or propositions. By attempting to break down problems into first principles and re-constructing solutions using these building blocks, you're less likely to be biased by prior assumptions. This in turn can lead to more innovative solutions.


  • A child repeatedly asking "why?" to answers for an initial question is intuitively thinking in first principles.

  • A company building a cheaper product than competitors by investigating ways of using the raw materials firsthand instead of just following existing conventions.

Proximate and Root Causes

Discovering the root cause of an event involves looking deeper than the immediate causes for that event.


A proximate cause is the event most closely associated with or immediately responsible for an observed result. This may differ from the root cause. Getting to a root cause often requires a deep dive into the situation using approaches like Socratic questioning or the 5 Whys


  • Post-mortem reports for critical failures generally outline proximate causes and how they stem from the root cause. For instance a website was down due servers running out of disk space which was in turn a result of a bug which in turn was a result of poor testing and so on.

  • A child repeatedly asking "why?" to answers for an initial question is trying to get to the root cause.

Social Proof

We tend to copy the behavior of others, especially during times of uncertainty.


Social proof is a term used to describe our tendency to follow the behavior of others. This tendency is amplified if we are uncertain about the situation. Social proof generally guides us into making fewer mistakes—if many folks are doing something, it’s usually the correct thing to do. However, this “auto-pilot” behavior can be easily exploited to manipulate our decision making process. For instance, to lead us towards a decision that serves someone else's interests or is incorrect.


  • Laugh tracks in TV shows and hired clappers in a theater performance can trick us into perceiving the content to be funnier or higher quality than it actually is.

  • Testimonials increase our likelihood of buying a product, especially when they indicate popularity. Terms like “best selling” or “recommended by 9 out of 10 professionals” are marketing applications of social proof.

Survivorship Bias

We tend to focus on things that survived and overlook things that didn't. This can lead to overly optimistic beliefs.


Survivorship bias occurs when we develop a skewed view of a situation by concentrating on the people or things that survived. Things that didn't survive lack visibility and are overlooked. A common result of survivorship bias is overly optimistic beliefs. By focusing primarily on the success stories, we fail to fully understand why the "failures" did not survive, often just assuming that it's due to a lack of qualities found in the survivors. Looking for counter examples when deriving patterns from success stories can be a useful exercise in combating survivorship bias.


  • We often attribute the success of famous entrepreneurs solely to their behavior and overlook things like luck and timing. By ignoring the failed companies that followed similar approaches, we might be overly optimistic about the likelihood of our own entrepreneurial success.

  • It's easy to perceive music from the past as being higher quality than contemporary works. Music from the past, however, has gone through a selection process where higher quality works have survived. With contemporary music, we hear the mediocre along with the good.


We tend to feel obligated to repay positive actions towards us (e.g. favors, gifts) even if they are unwanted.


Reciprocity refers to a social norm in which we feel a sense of obligation when receiving positive actions towards us. For instance, receiving a favor or gift can trigger feelings of indebtedness to repay the act in someway. While reciprocity allows one to build relationships and exchanges, it can be exploited to gain someone's compliance to a request. This is because feelings of obligation can be felt even when receiving a positive action we do not want.


  • Before attempting to sell something, a salesperson may give you a small gift (e.g. a pen or a free sample). Even if this gift is unwanted, receiving it can still trigger a need to repay the gift, usually in the form of purchasing whatever is being sold.

  • A common compliance technique is to start by making a large request that's likely to be rejected followed by a second, smaller request. The second request, which is the intended request, is more likely to be accepted as it's seen as a favor.

Hindsight Bias

The feeling that we could have predicted an event after it occurs (i.e. we "knew it all along").


Hindsight bias is the feeling we get when we perceive an event as being predictable, even though there's little evidence to suggest we could have predicted it. Once the event has occurred, it's easy to work backwards and find explanations. While hindsight bias can result in increased confidence and performance, too much can lead to overconfidence and an inability to learn from experience. For instance, by assuming that we could have done better than others after knowing the results of their actions, we lost an opportunity to understand why those actions were made.


  • In court, judgement of a defendant can be clouded by hindsight bias. The jury, knowing the outcome of the defendant's actions, might feel as if they could have predicted the outcome.

  • We may feel that people in the past were less intelligent or innovative than those of the present without acknowledging that they did not access to present day information. Related: Historian's fallacy and chronological snobbery.

Confirmation Bias

We have a tendency to perceive things in a way that re-enforces or aligns with our preexisting beliefs.


Confirmation bias is a cognitive bias that causes us to see things in a way that confirms our preexisting beliefs. Because it involves selectively collecting and recalling information, the end result is a biased view point. In addition, confirmation bias may also cause us to ignore information that doesn't support our views. Closely related is the feeling of cognitive dissonance which refers to the discomfort we feel when holding contradictory beliefs.


  • In social media, we're often shown content that we're more likely to agree with. This amplifies confirmation bias--we only see things consistent with our beliefs resulting a sort of "echo chamber". For more on this, see filter bubbles.

  • Belief in farfetched conspiracy theories can often be a result of confirmation bias. If one tries hard enough, they can find things that seem to support the theory while ignoring the evidence that refutes it.


We tend to place higher value on things that are rare and lower value on things that are abundant.


Scarcity refers to our tendency to place value on things according to how rare they are. It's often used as a mental shortcut to assess the value of something based on how easy or difficult is it to acquire. Scarcity doesn't just apply to objects--it can also be applied to things like time and information. For instance, we might place high value on spending some time with a busy individual or getting access to confidential information. Since scarcity can increase our desire for something, it's often artificially created to sell something. A good strategy to combat this desire is to remember that scarcity only increases our desire to obtain something and doesn't affect the actual value we'll extract from it.


  • Sales techniques likes setting deadlines on promotions or indicating that limited quantities are available are designed to drive up scarcity driven desire for the item being sold.

  • When information is censored, we not only feel a stronger desire to know about it and but also tend to be more favorable to it.

Pareto Principle

For many scenarios, 80% of the effects stem from 20% of the causes. This is often referred to as the 80/20 rule.


In 1896, economist Vilfredo Pareto found that 20% of the population in Italy owned 80% of the land. This ratio is commonly cited in wealth distribution (the richest 20% owns the majority of the world's income) and in business management (80% of sales come from 20% of clients). Another application is managing workload--by prioritizing the 20% most important work, we can (at times) gain 80% of the value. Note that while the Pareto principle can be a useful construct in many situations, it's not applicable everywhere. See also: Power Law.


  • Microsoft once noted that fixing the top 20% of reported bugs would solve 80% of issues and crashes in a system.

  • Many companies find that majority of revenue comes from a small portion of the product. For example, video rental shops in 1988 found that 80% of revenue came from 20% of the titles.

Thought Experiment

We can explore a theory by imagining an experiment for it and thinking through its potential consequences.


A thought experiments is a technique used to explore a hypothesis, theory or principle by thinking through what its consequences would be. These experiments are not actually performed and are often impossible to set up. The intent is not to prove something, but rather to explore difficult questions through speculation and logical thinking. Hopefully, the results of this thinking will lead us down interesting paths we might otherwise miss. Some examples are: "What will happen if this event occurs?", "If B happened instead of A, how might things differ?", "If something happens in the future, what might cause it?".


  • Einstein imagined what would happen if someone chased a light beam and caught up. The results of this thought experiment lead him to special relativity. Note that this experiment was not actually performed and the theory was proven using other empirical means.

  • The trolly problem is a famous thought experiment in the field of ethics. It's often referenced with thinking about the design of self-driving cars.

Diderot Effect

Obtaining something new can lead us to purchase of additional, complementary things that we otherwise wouldn't have.


The Diderot effect is named after French philosopher Denis Diderot who, after receiving an expensive robe, began a purchasing spree because he felt his current possessions felt tawdry in comparison to the robe. The effect consists of two ideas. The first is that we purchase things which feel cohesive to our sense of identity. These items tend to be complementary. The second is that obtaining something that differs from our current possessions can result in a desire to obtain goods which complement the new possession (i.e. are consistent with this new identity). This can result in a spiraling shopping spree.


  • Moving into an expensive house often leads to the purchase of new furniture and household goods even if our old furniture is fine. We feel a desire to upgrade our furniture in the same way we've upgraded our house.

  • Marketers often attempt to appeal to a desired identify when advertising their products. For instance, certain brands are associated with an active / health conscious image. We are likely to purchase these items if they appeal to our personal sense of identity.

Map and Territory Relation

While models are useful in explaining reality, they are not reality itself.


Often described as "the map is not the territory", this mental model refers to the relationship between an object and a representation of that object. A map is an abstraction and imperfect representation of a territory--it is not the territory itself. Abstractions are a necessary step in simplifying the complexities of reality. After all, imagine how difficult it'd be to drive in an unknown area without a map. However, we should be aware that these abstractions have limitations and are created using assumptions that may not always be true. This applies to mental models as well--while useful in explaining common situations, reality is not bound to conform to these models.


  • Newton's laws of motion are a model explaining physical phenomena. While an excellent approximation for most cases, these laws do not hold when working at very small scales, at very high speeds, or in very strong gravitation fields. These cases require different models.

  • The Treachery of Images is a famous painting of a pipe with a caption stating this is not a pipe. In describing it, painter René Magritte said, "...could you stuff my pipe? No, it's just a representation, is it not? So if I had written on my picture 'This is a pipe', I'd have been lying!"

  • This classic clip from The Office of Michael Scott driving into a lake is a literal example of the map not being the territory.

Gambler's Fallacy

The mistaken belief that a random event is more or less likely to occur based on past outcomes.


Past occurrences of an independent random event have no impact of future occurrences. For instance, the probability of getting heads in a coin toss is 1/2 regardless of the previous tosses. If we encounter a dozen heads in a row, we may feel that the next toss will be tails to balance things out. This is a mistaken belief--the probability of tails remains 1/2, the same as in previous tosses.


  • A game of roulette at Monte Carlo Casino on August 18, 1913 is perhaps the most iconic example of the fallacy. The ball fell in the black 26 times in a row causing gamblers to lose millions in the mistaken belief that the probability of red was now higher.

Goodhart's Law

When a measure becomes a target, it ceases to be a good measure.


Goodhart's Law highlights the issue with focusing solely on the value of a measure as an indication of success or progress. Often, observers will artificially change their behavior to reach a target without caring about the reason for the measure. In other words, they'll try to game the system. The law was originally stated as: "Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes."


  • Google's PageRank algorithm would rank websites based on the number of incoming links from other websites. This led to webmasters gaming the system by artificially increasing the number of links to their website.

  • A company requiring writers to write a specific number of words a day will probably produce low quality, filler content as writers try to meet their quota.

Sunk Cost Fallacy

We have a tendency to continue an endeavor after investing resources into it even if it's no longer worthwhile.


The sunk cost fallacy describes our resistance to stop an endeavor after investing time, money or effort into it. This limits our ability to see its worth in present terms and potentially misallocate additional resources on it. In other words, we're not cutting our losses. Ideally, we would make decisions regarding an endeavor based on relevant information--suck costs are almost always irrelevant.


  • When selling a used car, the amount originally paid should have not factor into the decision to sell it. Rather, the decision to sell the car should be based on if the owner will get more value from selling it at the current resale price versus keeping it.

  • When working on a business that's not picking up any traction, we may feel obligated to continue due to amount of time and money we've poured into it. That effort is a sunk cost, future decisions regarding the business should ignore it. See also: escalation of commitment.

  • Leaving in the middle of a sports game might feel like we're wasting the money spent on the ticket. However that money has already been spent, it should not impact future decisions.

Diminishing Returns

In productive processes, the value gained from increasing one input but keeping others the same will at some point start decreasing.


When producing something, there are inputs and results. The law of diminishing returns states that simply increasing one input but keeping others the same will at some point yield diminishing results. In some cases, this can be improved by adjusting other inputs appropriately. For example, if adding more workers to a factory, we can also add more machines and working space. In other cases, the production may be inherently difficult to parallelize.


  • Brook’s law states that just increasing headcount in a software project, will not make it ship faster. Ramp-up time, communication overhead, and the indivisibility of certain tasks may in fact slow it down.

  • In our personal lives, we may find that doing too much of something may lead to diminishing (or even negative) returns. For instance, over editing a piece of writing or continuing to tweak a painting.

Recency Bias

We tend to place greater emphasis on recent events over past ones.


Events that have occurred recently tend to be seen as more important than historic events. This is often just because the event is fresh in our memory as opposed to its actual importance. Given that the perceived importance of recent events will likely drop with time, recency-bias can lead to skewed perceptions and poor decision-making.


  • Employee reviews are prone to recency bias. The performance of work done most recently will disproportionally impact the final review.

  • In Law, the closing argument given by the defense is seen to have an advantage as it's the freshest in the jury's memory.

Premack's Principle

More desirable behaviors can be used to reinforce less desirable behaviors.


Premack's Principle, often used in psychology, suggests that more desirable activities can motivate and reinforce less desirable ones. It's based on the idea that if a person wants to do a particular activity, they can use that desire as a reward for completing a less appealing task first. This principle is especially useful in behavior modification, education, and self-discipline strategies, helping individuals or educators to encourage the completion of necessary but less appealing tasks by following them with more enjoyable activities.


  • A child who enjoys playing video games can be encouraged to finish homework first, using game time as a reward.

  • An employee who loves coffee breaks can use the break as a motivation to complete a challenging report.

Goldilocks Rule

Optimal motivation occurs when tasks are neither too hard nor too easy.


The Goldilocks Rule states that maximum engagement and motivation are achieved when tasks are at the right level of difficulty - not too easy to be boring, but not too hard to be frustrating. This concept is rooted in the psychological theory of flow, where a person is fully immersed and focused on an activity. The Goldilocks Rule is valuable in personal development, education, and workplace productivity, as it helps in designing tasks and challenges that keep individuals optimally engaged and motivated, leading to better learning, performance, and satisfaction.


  • In education, tailoring lesson difficulty to match a student's skill level increases engagement and learning effectiveness.

  • In the workplace, assigning projects that are challenging but achievable boosts employee motivation and job satisfaction.

Illeism (Third Person Thinking)

Referring to oneself in the third person can create psychological distance and objectivity.


Illeism is the practice of referring to oneself in the third person (e.g. they) instead of the first person (e.g. I). This can be used as a mental model to create a psychological distance between the self and one's actions or thoughts. By speaking or thinking about oneself as a separate entity, it becomes possible to assess personal behaviors, decisions, and characteristics more objectively. This detachment can aid in self-reflection, reduce emotional bias, and foster clearer, more impartial thinking. It's a technique sometimes used in therapeutic settings, leadership development, and by public figures to gain unique perspectives on their own actions.


  • Instead of thinking "I need to improve my work performance," considering "John needs to improve his work performance" to gain a clearer perspective on the steps to be taken.

  • A public speaker preparing for a presentation might think, "How would the audience view Maria's speech?" to refine their approach and content.

Hyperbolic Discounting

People tend to choose smaller, immediate rewards over larger, later rewards.


Hyperbolic discounting is a cognitive bias where individuals prefer smaller, immediate rewards to larger, delayed ones. This model explains why people often opt for immediate gratification, even when waiting would yield a better outcome. This behavior is contrary to the "rational" choice model in economics and highlights the human tendency to disproportionately value the present over the future. Understanding this bias can help in making more rational long-term decisions, such as saving for retirement or maintaining healthy habits.


  • Choosing to spend money on a luxury item now rather than saving it for a larger purchase or investment in the future.

  • Opting for an unhealthy snack for immediate satisfaction, despite long-term health goals.

Lindy Effect

Things that have been around for a while are likely to continue to stick around.


The Lindy Effect is a theory that suggests the future life expectancy of non-perishable things, such as a technology, an idea, or a book, is proportional to their current age. This means the longer something non-perishable has been around, the longer it is likely to continue to exist. This concept is often used to discuss the longevity of cultural items or technologies, suggesting that those which have proven their durability over time are likely to remain relevant or in use for an extended period.


  • Classical works of literature, like those by Shakespeare, having been around for centuries, are likely to remain relevant and read for many more years.

  • The QWERTY keyboard layout, despite its inefficiencies, has been in use since the 19th century and is likely to continue being the standard due to its widespread adoption and familiarity.

Zeigarnik Effect

We tend to remember unfinished tasks better than completed ones.


The Zeigarnik Effect is a psychological phenomenon that suggests people remember uncompleted or interrupted tasks better than completed tasks. Named after Soviet psychologist Bluma Zeigarnik, who first studied the phenomenon, it implies that incomplete tasks create a kind of mental tension that improves recall. This can be applied in various fields, such as education and project management, to enhance productivity and learning by structuring tasks and breaks effectively.


  • Students are more likely to remember the contents of a study session if they take a break in the middle, leaving some material unfinished until they return.

  • Cliffhangers in TV shows and books exploit the Zeigarnik Effect by leaving the audience eagerly anticipating the resolution in future episodes or chapters.

Endowment Effect

We tend to value things we own higher than we would if we didn't own them.


The Endowment Effect is a cognitive bias that causes people to ascribe more value to things merely because they own them. This effect suggests that people are more likely to retain an object they own than acquire that same object when they do not own it. This bias can lead to irrational decision-making in various contexts, from personal possessions to financial investments, where owners overvalue what they own and demand more to give them up than they would be willing to pay to acquire them if they did not own them.


  • A person might refuse to sell a family heirloom at market price, valuing it more due to its personal significance and ownership history.

  • Investors might hold on to stocks or real estate longer than rational analysis would suggest, simply because they own these assets and overvalue them compared to if they were potential buyers.

Parkinson's Law

Work tends to expands to fill the time available for its completion.


Parkinson's Law is the adage that "work expands to fill the time available for its completion", suggesting that the duration of a task is dictated by the deadline set for it, rather than by the amount of work involved. This concept implies that if you give yourself a week to complete a two-hour task, then (psychologically speaking) the task will increase in complexity and become more daunting so as to fill that week. It highlights the inefficiencies in time management and suggests the importance of setting appropriate deadlines to increase productivity.


  • A student given two weeks to prepare a presentation will likely use the entire period, even if the actual work could be completed in a few days.

  • An employee assigned a minor task with a long deadline might over-complicate the task, making it more time-consuming than necessary.