Socrates was taken aback when the Oracle of Delphi said there was none wiser than he. Not believing the Oracle, Socrates went on an exhaustive hunt for a person wiser than himself, but came up empty. Why? Because everyone he met thought that, because he knew his own craft really well, he knew everything really well.
Source: When Ricky Gervais Meets Socrates: A Lesson on the Limits of Knowledge | Antony Davies, James R. Harrigan