He describes the struggle for knowledge and the form of the Good. Plato illustrates in his dialogue human beings in an underground den, with an opening at one end that leads to the outside light. Each one of the human beings has been captive in the den from childhood, their legs and necks chained so they cannot leave, but only look straight forward. Behind them a fire burns with a wall that separates them from it. Periodically, people will pass along the wall carrying various objects, statues, and figures of animals creating shadows on the wall in front of the prisoners. In effect the shadows have become the reality of the prisoners, for it is all they have ever known. This reality keeps the prisoners in the state of ignorance, because their reality is based on illusions.
Comparing Truman to the person in the hypothetical argument, Truman was chained in place, not only to be subject to, but also to believe in Christof's imaginary world. Truman did not have the natural opportunity to suspect his reality was fake, a shallow, manufactured knowledge of life, until the illusion became impossible to continue. As soon as Truman became aware of his artificial existence, his true reality became to take form. He never suspected otherwise until the illusion began to crack. For him, that was reality. Throughout the movie many symbolic factors arise that can be related to the Cave Allegory, such as the actors, the director, the town, and Truman's fears.
The actors that take part in the Truman's life symbolize the shadows passing on the wall of the cave and their lines are merely the echoes created by the passer-by. They are the reality that Truman has grown to believe as the truth. The director, Christof, also plays an extremely significant role of a god-like entity. His office is above the stage, or from Truman's point of view, the heavens. When the director speaks to his star actor, it is in a voice of power, confidence, and all-knowing much what one might expect from a high being.