Disappointment is one of the most common feelings that anyone wants to reduce. You should accept that you cannot reach success without failure. You should get rid of the negative disappointment by changing the way you think.
Most relieving facts that may help you to change the way you think when you are in disappointing situation:
1-Any failure is step on the way of success
2-You may be dreaming of unattainable perfection. No one can be perfect.
3- You must live your life with those in your hand and with the actions you can achieve at that time. You can of course reach the goal you missed another time, there is always chance. Because it is very important to know that you are happy with what you have and to be at peace with yourself.
Besides that, you can change the disappointing situations with what you have.