Here's something else I'd like your opinion about," I said. "If he went back underground and sat down again in the same spot, wouldn't the sudden transition from the sunlight mean that his eyes would be overwhelmed by darkness?" "Certainly," he replied. "Now, the process of adjustment would be quite long this time, and suppose that before his eyes had settled down and while he wasn't seeing well, he had once again to compete against those same old prisoners at identifying those shadows. Would he make a fool of himself? Wouldn't they say that he'd come back from his upward journey with his eyes ruined, and that it wasn't even worth trying to go up there? And would they -- if they could -- grab hold of anyone who tried to set them free and take them up there and kill him?
Plato, The Republic
perception