Habitual and optimal, never shall they meet.

As I walked into the bathroom I flicked the light switch as I swung the door shut with a flick of my heel – efficient. Only the light was already on, so with great efficiency I succeeded only in plunging myself into darkness.

The more we repeat an action, the more unthinking that action becomes. This frees us to turn our minds to other things rather than being wholly and perpetually absorbed with the same mundane elements of our routines, but it also opens us up to a whole new class of human error. When I flicked the light switch (off), some part of me will have been aware that the light was already on