The allegory being referred to is Plato's Allegory of the Cave. In his work The Republic, Plato likened people untrained in the study of philosophy to prisoners chained in a cave, unable to turn their heads. All they can see is the wall of the cave, upon which shadows of objects outside are projected by a fire behind them. The shadows are the closest they ever get to seeing reality. One prisoner is freed, turns around and sees the fire, then journeys outside and sees the true forms of nature and objects. Upon returning to the cave, the once-freed prisoner tries to convince the other prisoners of the truer world outside, but they laugh and don't believe him. The allegory is meant to