The sensation of disappointment is fairly frequent among people, but what differentiates it is the source of the disappointment; most of us have and have felt it to be ourselves.
The most common question that arises in our minds is whether we are good enough, followed by past mistakes, and finally the classic self-blaming game that we frequently play. Although it is out of your control, the three steps that you take when you are dissatisfied with yourself do nothing to help you. However, it causes you additional pain and, truthfully, adds more gasoline to the fire.
We must recognise that we are not ideal confirmation coded robots that perform every duty flawlessly according to the coding, but rather that we are humans, and that every action and decision we make, whether good or bad, is based on the feelings we carry. Making mistakes is a part of growing up and evolving into a successful person and a decent human being. No one in the world has ever woken up flawless, and it is their mistakes that have led them to where they are now.
Disappointment is a natural part of growing up, but the sooner you consider the causes and stop blaming others, the better your life will be.