To criticize someone or something by pointing out their mistakes or problems.
From Old English 'findan' (to discover) combined with Old French 'faute' (lack, defect). The phrase emerged in Middle English as a way to describe discovering imperfections in something.
Finding fault is so common that it became a single phrase—our brains love bundling frequently-used ideas together. Languages do this constantly, creating idioms that say in two words what would take ten to explain literally.
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