There are four types of men in this world: 1. The man who knows, and knows that he knows; he is wise, so consult him. 2. The man who knows, but doesn’t know that he knows; help him not forget what he knows. 3. The man who knows not, and knows that he knows not; teach him. 4. Finally, there is the man who knows not but pretends that he knows; he is a fool, so avoid him.