War games do something seriously unpleasant to our brains

Three years ago, I killed several thousand people over the course of a single weekend. Late into the night, I ran around butchering everyone I saw, until by the end I didn’t even feel anything any more. Just methodically powering through it all, through the wet sounds of splattering heads, bodies crumpling, shiny slicks of blood. I thought I was past caring. But when I finally went to bed, I couldn’t sleep, and in my dreams I was haunted by all the men I’d killed. I saw their brains exploding, again and again and again.

In my defence, I’d had a bad week. It was December: a grotty English winter, not particularly cold but still utterly grim. The kind of winter that seems to stick to everything, like a layer of congealed grease. I was worried about money. My political party had just been utterly humiliated in a general election.