Full Idea
You could argue that a man cannot discover what he does know or what he doesn't. The first needs no discovery, and how do you begin looking for the second?
Gist of Idea
You don't need to learn what you know, and how do you seek for what you don't know?
Source
Plato (Meno [c.376 BCE], 80e)
Book Reference
Plato: 'Protagoras and Meno', ed/tr. Guthrie,W K C [Penguin 1956], p.128