Self-fulfilling prophecy

A self-fulfilling prophecy is when a person (or group of people) thinks something is true, and then behaves in a way that makes it actually true. It's like a magical prediction that comes true because of the person's behavior. For example, let's say your teacher tells you that you're going to do great in math. You believe it, and you work really hard on your math homework. Because of that, you really do do great in math! That's a self-fulfilling prophecy.