Learning to bounce back and let the disappointment go is key. When I realize I have attached an outcome to an event or action I have taken, I try and clear my mind of any desire for a specific out come and say to myself let what will be, be. I still have not been one hundred percent successful, I am human after all. Learning non attachment has helped me to limit my times of disappointment.
The other problem with disappointment is looking back. I want my focus to be on the road ahead and when I let disappointment drag me down and think about what could have been. I am using my precious life energy on something that I had dreamed up but is not real. I might have placed an expectation for a great outcome to an event to only be disappointed. Then I spend time thinking about what could have been. Letting go, not looking back will also help to keep disappointment to a minimum. Look at the road ahead, focus your energy on the present moment and disappointment will disappear.