Mirror

A mirror is a two-way dimension, because when you look into any mirror you just see yourself in the mirror. The other side of the mirror shows you in a different life where you keep on making doubles of yourself. Then, your double goes inside the real you, and you're living your double life while you're living your own life at the same time, until you get the double out of you. If you don't want to get the double out, you won't be able to live a normal life while the double is inside of you. You can send your double on a mission where the thing that made you double turns the double into dust; then you won't have to deal with the double. Or, you can keep your double inside of you to decide which kind of life you want, and nobody's going to decide for you because they're making the same decision. Everybody in the world has a double, and everybody in the world has to decide what they're going to do with their double.