Three prisoners gaze at the shadows on the wall, never having seen anything else before. This is what they believe is reality; just the reflections on the wall.
One of the prisoners is forced to be taken away, but as he looks away from the shadows he has know all his life, he denies it and resists as much as he can.
They exit the cave, and the prisoner's eyes are blinded and he is shocked when he is told that THIS is reality, not the shadows on the wall.
He explored the world and eventually got accustomed to the new environment, and was astonished at his new discoveries.
Finally, he became at home in this previously unknown world, and was able to look at the sun without hurting his eyes.
When telling the prisoners of his adventures, he mentioned that he did not see the shadows as clearly as he did before he left the cave. When they heard this, they thought he had gone man and vowed to kill anyone who tried to take them out of the cave.