The weirdest thing about sleep isn’t that you switch off for a third of your life. It’s that this switch-off is totally necessary, even though no one really knows why.

It makes sense to clean out the brain or boost memory as you go—like breathing or blinking. But why did nature pick a hard stop, like the whole being has to vanish from the world for hours at a stretch? Maybe we don’t sleep for the usual reasons. Maybe the very fact that we can’t stay awake all the time—that’s the whole point of sleep.