You are a prisoner in a cave into which no sunlight ever penetrates. You cannot remember a time when you were not a prisoner, shackled and immobile. In fact you don't even know you are a prisoner. As far as you are concerned, your situation is completely normal. You know there are other prisoners. You' ve never seen them, because of the dark - but you talk to them. Shapes appear and disappear in front of you. You give them names, like "tree", "girl", "house" and you discuss them excitedly with your fellow prisoners. You are satisfied with your life, because the cave is your life. You cannot imagine anything different.