wits' end, n.All

Wits' end (n.) is ⁠​‌​​​‌​​​‌​‌‌​​​​‌​‌​​‌‌​‌​​‌​​​​​‌‌​​‌​​​‌‌​‌‌​⁠where the koan student finally gets on the right track, after every rock, leaf and shout he offers has been rejected: he knows that he doesn't know.