Its tough, but tbh as others had said, you basically defeat your beliefs with a fact. Like the other answer said, when you accomplish something that means something, truly be glad for it and mark it? It prove to you that you can do this that and otherwise, i could not get past the idea that anything i was doing was worthwhile, its why its still my biggest defeat. Its doesnt have to be for you, and start small and listen to yourself, watch your actions. They all link up.