It’s Tuesday morning, and you have an eight-minute walk to a class that you will officially be late for in three minutes. That’s when you look up and see something. Your bedroom lights are on, and you won’t be back in the dorm for another seven hours.

For the next few milliseconds, you weigh your dilemma. On the one hand, leaving your lights on throughout the day slowly wastes electricity. On the other hand, you would surely be late if you went all the way back to your room to flick...