Does not succeed at something or stops working properly when you need it to.
From Old French 'faillir' meaning to be lacking or to fail, derived from Latin 'fallere' meaning to deceive or disappoint. The meaning evolved to describe any lack of success.
Interestingly, 'fail' originally meant to be deceived or disappointed, so when you fail at something, you're etymologically being let down—which is exactly what failure feels like!
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