Definition
Occam's razor holds that when several explanations fit the same facts, the one requiring the fewest assumptions is usually preferable. It is not a law of nature but a rule of thumb — a way to choose where to place your initial bet.
The reasoning is probabilistic. Every extra assumption an explanation depends on is another thing that could be wrong. A simpler account has fewer such failure points, so it is, on average, more likely to be correct and easier to test.
Why it matters
How it works
When you face competing explanations, count the assumptions each one quietly relies on. Favor the leaner account as your working hypothesis, then test it. If the evidence forces additional complexity, accept that complexity — the razor never asks you to ignore facts.
The tool is most powerful as a check against overfitting: it stops you from preferring a baroque explanation simply because it is more interesting or flattering.