This is usually said when the child already feels bad. You can be disappointed in everything in this world, but never in your own child because you are there to lead them on the right path. Guide them back when they do something wrong and teach them and explain then what was done wrong and why.
You’re not (something) enough
With this, you show the children a restricted image of themselves, implying that they lack in something in order for them to be who they want to be or do what they want to do. They’re enough to be themselves and they need to grow to become what they are. Tell them to practice or train something before so they will grow that way.