During Socrates’ trial as described in The Apology, we learn that his friend Chaerephon had asked the oracle of Delphi if there was anyone wiser than Socrates—and that the omniscient priestess replied that there was not. As a test, Socrates then asked three classes of Athenian men who were all highly esteemed for their wisdom—politicians, poets, and skilled craftsmen—about wisdom and knowledge.
In questioning the politicians, he found that though they thought they were very wise, they did not in fact know much of anything at all.
Although the poets wrote great works of genius and seemed incapable of explaining them, Socrates concluded that their genius came not from wisdom but from some sort of instinct or inspiration which was in no way connected to their intellect. Furthermore, Socrates found that the poets seemed to believe that they could speak intelligently about topics of which they were quite ignorant.
Finally, in the craftsmen Socrates found men who truly did have great wisdom in their craft, but invariably, they seemed to think that their expertise in one field allowed them to speak authoritatively in many other fields—fields about which they knew nothing.
As a result of this investigation, Socrates affirmed that he would rather be as he is—knowing that he knows nothing—than to be inflated by a false sense of his own great wisdom. Thus, Socrates concludes that he is indeed truly wiser than other men and that this is because he does not think he knows what he actually does not know.