Keywords: reality, shadows
Assuming there are people who live and are chained in a cave since birth, and everything in our world proceeds behind them. They only look at the shadows of those things cast by candle light on the cave wall in front of them. They would necessarily regard the shadows as reality. If one day, one of them escapes from the cave and look directly at those things which are cast into cave, that person would realize the shadows are not reality. When that person returns to the cave to narrate this finding to other people in the cave, they would not believe it and still consider the shadows to be reality.
The above parable is not just to let us think about the things contained in our life. It is also to imply that we are not able to identify whether this world that we regard as reality is a real reality or not.
Thus, here we can obtain a conclusion that everything in our world, or specifically speaking, the physical world which we think is the most real is a mere shadow of a higher reality.