Rebound effect

The rebound effect happens when you do something, and then something else you didn't expect happens as a result. For example, let's say you try to save energy by turning off the lights when you leave a room. But then, because it's now darker in the room, you turn on a lamp, which uses more energy than the original lights. This is the rebound effect, because you didn't plan for the energy you used when turning on the lamp.