Did not get William Shakespeare's quote - "A fool thinks himself to be..."

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?

Solution 1:

I believe it relates to this quote by Confucius

“True wisdom is knowing what you don't know”

― Confucius, Sayings of Confucius

The realization that the self is lacking, that there is always more to learn and that one doesn't know nearly everything, or even as much as what one thinks he knows is the hallmark of the wise man. He knows that he still has much to learn (there are other cultural idioms which express this).

Solution 2:

Origin: This line is from Shakespeare's comedy 'As You Like It' (5.1) spoken by Touchstone, who is a Fool in the play, to William.

• The irony is that Touchstone is a fool, yet he is counselling William that;

i ) A Fool who is being foolish and understands that his actions and behaviour are only an act of folly makes him wise, whereas a person who is being foolish and does not realist this is a true fool.

ii ) Only a fool would think himself wise enough, or consider himself a wise man, whereas a wise man thinks himself as a fool because he understands the concept that there is always more to know and more to learn.

iii ) Fools had the license to make offensive comments on members of the court, and more importantly on the monarch. It thus takes much wit to make use of this privilege/power, and Fool in the day, and in Shakespeare's plays have been considered the one who can see clearly, and is more knowledgeable (a fool always presents himself with folly, thus no one actually ever knows how much a fool knows).