It's not unusual to feel certain emotions without knowing why. Disappointment is not one of those emotions. When we feel disappointed, we almost always know what caused it...
Disappointment stems from positive expectations that never materialize or from desires that are left unfulfilled. We expect something to go a certain way and it doesn't; we feel disappointed. We want something badly but aren't able to have it; we feel disappointed.
Ideally and over time, we can learn to transcend disappointment. To do this, we must let go of our attachment to ideas about how things "should" be. When we stop clinging to our expectations, we are able to accept with equanimity whatever the present moment contains.
Many people never realize this truth. Even among those who strive to let go of expectations, there are few who will attain this ideal. As a result, the great majority of us will continue to experience disappointment throughout our lives -- disappointment in ourselves, in our circumstances, in outcomes, and in others. For us, the task becomes finding a way to work through disappointment so that we can move past it.
Disappointment is one of those emotions that can become toxic if left unaddressed. Long term, chronic disappointment in oneself leads to feelings of worthlessness and self-loathing. Enduring disappointment in someone close to us causes anger and resentment towards that person. Perpetual disappointment in life or its circumstances leads to feelings of hopelessness and despair. These emotional states can quickly develop into habitual ways of relating to ourselves, other people, and the world.
These are all things I know and can pass on to others without difficulty. It is one thing to know; it is another to do...which is what I am struggling with now.
I believe that acceptance is the antidote to disappointment. To feel disappointed is to wish the present moment to be something other than it is. Therefore, the first step in overcoming disappointment is to accept reality as it is.
Sometimes letting go of disappointment feels like giving up. For example, if we give up on pushing our child to work hard and be responsible (because we've had so many arguments about it but nothing ever changes) are we giving up on our child? It can certainly feel that way.
But isn't the pushing just a way to avoid facing our disappointment? Isn't it our attempt to get our child to do what is right so that we can be proud of him? Nobody wants to say, "My son dropped out of school and refuses to get a job." To have invested so much of our time, energy, and love into raising a child who then refuses to become a productive member of society is a great disappointment. So we refuse to accept it. We push our child to do what is right. We will not allow our child to fail. It is simply not acceptable.
What happens when we do this for months and then years without success? We've probably had so many fights with our kid about it that he's stopped coming to visit. We worry about it constantly and think about what else we can do to change things. We feel angry at and resentful towards our child for letting us down. In short, we suffer.
This is when it becomes time to accept. Sticking with my example, the time has come to accept that our child is a bit lazy and doesn't care much about becoming a productive member of society. Yes, it's disappointing; but once we've stopped trying to change our child and have accepted him as he is, we can then grieve the loss of what we wanted him to become.