Definition
Simplicity, often associated with Occam's razor, is the principle that among competing explanations or solutions, the one with the fewest assumptions and moving parts is usually preferable. It does not claim the simple answer is always true — only that it is the most reliable place to start.
As a mental model, simplicity is a bias toward economy. It treats every added assumption, feature, or component as a cost that must be justified, because each one is another thing that can be wrong or can break.
Why it matters
How it works
The model is applied as a tie-breaker and a discipline. When two explanations fit the same facts, the one requiring fewer untested leaps is favored until evidence forces the more elaborate one. When designing a process or a tool, each element is questioned: does this part earn its place, or is it there out of habit?
Simplicity is not the same as crudeness. A simple solution must still account for the full evidence — discarding necessary detail is oversimplification, not economy. The skill lies in finding the leanest version that still works, then resisting the slow accumulation of complexity that erodes it over time.