Imagine you have a magic mirror. What does it reveal about anyone who looks in it?
It would reveal you as the best that you can be, in every way: intellectually, and in terms of personality as well as physically. Thus if you're heavy, you'd see what you'd look like slimmer, and if you're harsh, you'd see what life would be like if you were kinder; if you're slothful, you'd see how your life would be if you were industrious, and so on. I don't know that I'd dare to look in that mirror!