Knowledge is hard to come by; it is also supremely important in human life. That is a theme that Plato finds in Socrates, and he never renounces it. In his many investigations of knowledge Plato develops many puzzles and insights about its nature. Socrates was told by the Delphic oracle that he was the wisest man in Athens. Although he received the news with incredulity, out of piety he put it to the test by sounding out those in the city who were reputed to be wise. Under the pressure of his dialectical examinations they turned out to belie their reputations. Socrates concluded that he was wiser than all of them. For while they knew nothing, and he also knew nothing, he at least unlike them knew that he knew nothing. This gave him the advantage and justified the oracle's claim.

Strictly speaking Socrates' claim is incoherent. If he knows that he knows nothing, then he knows nothing: not even that little bit that gave him the advantage over the pretenders. But if he does indeed know nothing, then he lacks the piece of knowledge that led to the little paradox of the previous sentence. Plato was impressed by Socrates' evident commitment to the life of reason and argument, which certainly put him ahead of any contemporaries in that respect. That was one insight that Plato took from his acquaintance with Socrates.