>>37199
Plato's Cave.
A bunch of people are chained up in a cave (or in The Matrix, that movie was basically Plato's Cave with explosions), and the only thing they see are the shadows cast by a fire behind them. They can't see the fire, nor can they see anything other than the shadows, so they assume the shadows are the real world.
If someone breaks out of those chains, and gets out of the cave, and tries to explain the outside world to the people inside? He's considered insane.
Of course, there's a reason that the people in the cave assume that their world is the real one. If you try to live on the assumption that none of what you see, feel, or experience is real, then you end up paralyzed because you can't figure out what is real. Thus, you end up being unable to function as you try to plan for the event that your computer is actually a cactus.