at one's wit's end

at (one's) wits' end

In a state of distress because one has no more patience or mental stamina, often after having dealt with some kind of problem or difficult situation. The baby's been crying for hours, and I'm at my wits' end! I'm already at my wits' end, so if this train gets delayed too, I'm going to scream.
See also: end

at one's wit's end

Also, at wits' end. Completely puzzled and perplexed, not knowing what to do. For example, I've tried every possible source without success, and now I'm at my wit's end. This idiom, which uses wit in the sense of "mental faculties," appeared in Piers Ploughman (c. 1377).
See also: end