At one’s wit’s end

The earliest text that refers to people being at their wit’s end is William Langland’s Middle English narrative poem The vision of William concerning Piers Plowman, 1370-90:

Astronomyens also aren at hir wittes ende.
[Astronomers are also at their wit’s end.]

By ‘wit’ Langland didn’t mean the facility to deliver sparkling and amusing dialogue, like Oscar Wilde or Noel Coward. The wit in ‘wit’s end’ was a more general mental facility.

Langland had described a situation that was perplexing to all-comers, both “those of the flood and the land – shipmen and shepherds” and that, even those who look outside our world (astronomers), didn’t know what to do.

The expression also appears later in the Bible, Psalms 107:27 (King James Version):

They reel to and fro, and stagger like a drunken man, and are at their wit’s end.