Put yourself in a state of continuous and corrective attitude checks. This requires a realistic self-assessment of the thoughts you are having. During recent speaking engagements, I instructed the participants to swallow their pride to achieve their goals and dreams.
Find role models who will not allow you to feel self-pity or bitterness. Incorporate a get-over-it attitude that involves developing corrective action instead of internal mental struggle. One forces you inward and away from success, whereas the other provides a plan. Remember: Action feeds positive mental attitude.