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.