Picture this with me: a large elephant chained to a small post in the ground.
Maybe you’ve seen a similar sight? It’s a powerful visual. Why would a large and powerful elephant be held captive by something so small and insignificant?
It’s because of what that elephant has come to believe about himself and that post. If you tie an elephant to a post when he’s young, he can’t get away. If you do this regularly while he grows, he’ll continue to believe that he can’t escape, no matter how large he becomes.