When two explanations both fit the facts, the one requiring fewer assumptions is usually closer to the truth — and always easier to test and disprove.
Occam's razor: when explanations compete, prefer the one that needs the fewest assumptions — it's more likely true and easier to test.
Your code worked yesterday and breaks today. One explanation: a rare cosmic-ray bit-flip corrupted memory. Another: you changed a line. Both "fit," but one needs a pile of improbable assumptions and the other needs one. Bet on the line you changed.
The 14th-century friar William of Ockham is remembered for the principle now called Occam's razor: don't multiply assumptions beyond necessity. It isn't a law of nature — sometimes the complicated explanation is the true one — but as a default, the leaner theory is more probable and far easier to test, because it has fewer moving parts that could be wrong.
Faced with competing explanations, count the assumptions each one needs to be true, and start with the lightest. Test that first. You can always add complexity when the simple story fails — but you'll be right more often if you reach for it last, not first.
It's a fast, reliable default for cutting through competing theories — in debugging, diagnosis, and everyday reasoning.
Misread as "the simplest answer is always right." The razor only says don't multiply assumptions beyond necessity — prefer the simpler explanation when explanations fit the evidence equally well. If a simpler story ignores the facts, the razor doesn't favor it. It's a tie-breaker, not a truth oracle.
Lock this idea into memory with a 5-minute active-recall session — the science of spaced repetition, no signup.
Try this idea free →