Socrates

The unexamined life is not worth living.

Source: Plato, Apology 38a (c. 399–390 BCE)

Socrates' words as reported by Plato at his trial, Apology 38a: 'ho de anexetastos bios ou biotos anthropoi' — the unexamined life is not worth living for a human being. Standard, uncontested, and the single best-sourced Socrates quotation. Strictly speaking it is Plato's rendering of Socrates, who left no writings, but the attribution convention is universal.

Wikiquote

I am the wisest man alive, for I know one thing, and that is that I know nothing.

Source: The Republic – https://www.goodreads.com/quotes/534070-i-am-the-wisest-man-alive-for-i-know-one