From Plato’s Apology (Socrates speaking):
“I am wiser than this man: neither of us knows anything that is really worth knowing, but he thinks that he has knowledge when he has not, while I, having no knowledge, do not think that I have. I seem, at any rate, to be a little wiser than he is on this point: I do not think that I know what I do not know.”
Prometheus Unbound 