Socrates: Now, Glaucon, let's think about the ignorance of human beings and their education in the form of an allegory. Imagine them living underground in a kind of cave.... They see only the shadows the light from the fire throws on the wall of the cave in front of them.... So, it's obvious that for these prisoners the truth would be no more than the shadows of objects.... Now let's consider how they might be released and cured of their ignorance. Imagine that one man is set free and forced to turn around and walk toward the light. Looking at the light will be painful.... (Plato: The Republic. Book Seven)