There’s someone in the room with you; he’s unconscious, and what’s really odd is he’s identical to you in every way—he shares your DNA, your memories, your love of dubstep, Beethoven, and psychedelic drugs. He has all your scars. He’s felt all your humiliations, your embarrassments, your regrets. He is, at least from objective realities’ perspective, indistinguishable from you by every conceivable objective measure, e.g, the arrangement of his neurons, his reactions to identical situations, his thoughts in general.