A belief is nothing more than a thought that occurs numerous times. That thought then becomes what a person believes to be a truth.
A great tool for optimistic living is to train yourself to think different thoughts over and over again. Set up a ritual to be silent, and bring to your mind positive thoughts about situations that seem to be challenging. Think and FEEL the positive resolution.
Do it repeatedly. Make it a habit.
Thinking and feeling positively will formulate a different set of beliefs about those challenging situations. Go ahead, try it.
I dare you.