When the Delphic oracle said that "none was wiser than Socrates", Socrates realized that what the oracle really meant was:

According to Plato's "Apology," the oracle of Delphi once said that Socrates was the wisest man in Athens. Socrates believed that this was impossible, as he had no knowledge at all. He decided to test such a theory by going around and asking others whether they were wise. He realized that all people believed they had some knowledge. In a paradoxical way, Socrates realized that he was in fact the wisest person in Athens, as he was the only one who was aware of the fact that he knew nothing.