A brain injury can leave us unable to perceive an entire spatial area—everything to our left for example—leaving it always empty, like the abyss that precedes our birth. Or we can go so blind that we can no longer imagine seeing. But these things don’t usually happen in our lives, and never more than once. But the on and off of our sexuality, just as complete and just as astounding, happens frequently and we don’t give it a thought.
