Occam's Razor

Of two equivalent theories or explanations, all other
things being equal, the simpler one is to be preferred.

Occam’s (or Ockham’s) razor is a principle attributed to the 14th century logician and Franciscan friar William of Ockham. Ockham was the village in the English county of Surrey where he was born.
Source: Wikipedia.org

First heard of it while watching an episode of House.