A very well known quote by William Shakespeare
A fool thinks himself to be wise, but a wise man knows himself to be a fool.
The first half is okay – a fool thinks himself to be wise (he's in that misunderstanding to be wise). The second half made me scratch my head.
…but a wise man knows himself to be a fool?
What's that? Why a wise man would ever know himself to be a fool? What am I missing?