The only sure way to avoid disappointment is to avoid doing anything with your life. But then that would be the ultimate disappointment.
When you step forward, you will occasionally encounter disappointment. However, if you never step forward, your whole life will be a disappointment.
Disappointment happens, and yet it never has to stop you. Disappointment, as painful as it may be, is a normal part of a rich, successful and fulfilled life.
Things are not always going to go your way.