The allegory of the cave theme?

The allegory of all allegories, Plato's Allegory of the Cave is not the rosiest take on the reality of human existence ... "See human beings as though they were in an underground cave-like dwelling," instructs Socrates, "with its entrance, a long one, open to the light across the whole width of the cave" (514a). The Deets.

The main theme of Plato’s allegory of the cave is that we humans tend not to understand the true reality of our world.