This is the well-known statement attributed to the ancient Greek philosopher Socrates (c. 470-399 BCE) according to the two dialogues long ago written by his disciple Plato (c. 424-c.348 BCE) in The Republic (c,360 BCE). When concluding a discussion with Thrasymachus about Justice, Socrates says “the result of the discussion, as far as I’m concerned, is that I know nothing, for when I don’t know what justice is, I’ll hardly know whether it is a kind of virtue or not, or whether a person who has it is happy or unhappy”. Socrates repeats this form of statement in The Apology (390 BCE) by saying “he knows nothing, and thinks that he knows; I neither know nor think that I know”.
What he meant? He meant that knowledge is never really acquired.