Simile of the Cave... From Plato's "The Republic"
Imagine a cave with a long entrance open to daylight leading away. In the cave there are prisoners who have been there since birth. The are chained to a wall so that they can only see the back of the cave and not the light from the entrance.
Higher up and behind them there is a fire, kept lit by guards. Between the fire and the prisoners there is a path, which the guards walk along carrying things such as statues and wooden animals etc. And sometimes the guards talk and sometimes they dont. Imagine then that the shadow of these guards carrying statues and animals is cast onto the back wall of the cave by the firelight. The prisoners below can only see the shadows.
Imagine also that the voices of the guards echoes from the back wall, so to the prisoners it would seem like the voices would be from the shadows of the item, and to them the shadows would be reality. They take great sport in guessing what shadow is next, for that is all they see.
Then, one man is released and brought up from the cave to where the fire is. The light from the fire would surely burn his eyes, and he would see the items and he is told that this is reality and the shadows were false. He is then forcibly dragged up the long entrance and out into daylight. The brightness would surely blind him, temporarily at least.
The man has to watch the dark, which eventually becomes the man looking at shadows of people and items, he then will be able to look at reflections of reality in water, and eventually he will be able to gaze at the sky at night. Finally after years, the man can look at the sun and daylight, and learns mathematics and sciences and arts. He is then taken back to the cave and chained to the wall with his old prisoners. His eyes are unaccustomed to the dark so he is once again temporarily blinded. His friends ask him to predict the next shadow but he cannot see them yet and is ridiculed.
The man tries to explain that they are wrong, that reality is outside the cave, but the other prisoners continue to ridicule him and say that his venture out the cave left him blind and dumb. If the man then attempts to force the other prisoners to ascend the cave, they would surely kill him is they could lay their hands on him.
(Please read this Allegory and ponder what it means. I am looking forward to hearing your responses as the Cave Allegory can be applied to any circumstance and it would be most interesting to hear how people apply it to themselves, to others or to situations.)