While sleeping on my living room couch, I woke up sweaty in the middle of the night. Plus, to my annoyance, I needed to pee. So I got up to go to the bathroom, which was just a few steps away.

My floor light, which usually comes on to help me see my way at night, failed me. It was pitch black, and I had the same sharp, clear vision as Mr. McGoo.

I didn't panic, though. Even without my floor light, I thought I could make it to my bathroom. After all, ...