We all want to be alone from time to time, to escape the demands of our colleagues or the hassle of crowds. But not alone alone. For most people, prolonged social isolation is all bad, particularly mentally. We know this not only from reports by people like Shourd who have experienced it first-hand, but also from psychological experiments on the effects of isolation and sensory deprivation, some of which had to be called off due to the extreme and bizarre reactions of those involved. Why does the mind unravel so spectacularly when we’re truly on our own, and is there any way to stop it?