"Those who carry torches will pass them on to others."
-Plato, The Republic
Plato's philosophy is introduced allegorically in the "Myth of the Cave," which appears in his most important work, The Republic. There, he has Socrates conceive the following vision:
Imagine prisoners chained in a such a way that they face the back of the wall of a cave. There they have been, for life, and can see nothing of themselves or each other. They see only shadows on the wall of the cave.
These shadows are cast by a fire which burns on a ledge above and behind them. Between the fire and the prisoners there is a wall-lined path along which people walk carrying vases, statues and other artifacts on their heads. The prisoners hear the echoes of voices and see the shadows of the artifacts, and they mistake those echoes and shadows for reality.
Plato has Socrates imagine that one of the prisoners is unchained, turned around, and forced to look at the true source of the shadows--the fire, the torch.
But the fire pains his eyes. He prefers the pleasant deception of the shadows. Behind and above the mouth of the cave, and outside in the bright sunlight (only a little of which trickles into the cave) are trees, rivers, mountains and sky.....
Now the former prisoner is forced "up the steep and rugged ascent" (Plato's allegory of education) and brought to the sunlit exterior world. But the light blinds him, he must first look at the shadows of the trees (he is used to shadows) then at the trees and mountains..then finally, he is able to see the sun itself.