I deal with disappointment alot better as an older person than I did as a younger person. I don't expect too much from people anymore, and I know that outcomes can be random in any situation.
Also, I focus on solutions, instead of the problem. "Yep, this disappointment sucks, so how do we navigate through it?"
I am quite good at crying and think it really helps me stay sane when bad stuff is happening or it just isn't my turn for something good to come along. I can sort of cry to order and the aftermath is comforting. I think hormones might get released or something like that, that helps. also am up for taking a nap my partner lives upstairs to me and I ask him to wake me by knocking on the ceiling when its a certain time.
I roll with it. Disappointment only seems possible with anticipation, or expecting things in advance, to go a certain way.
I found if I simply leave my mind open, and don't fill in the unknown , life goes far easier.
For example : everything cycles. Homes, vehicles, relationships, jobs, our bodies, weather, all aspects of life. They hum along fine - sometimes for so long we take them for granted - until such a time as they don't. Maintaining, and being as prepared as possible for the inevitable, also makes life easier.
Expect the unexpected , and know that all sorts of things can change in mid-flight - whether you want them to, or not ! Eh !
I examine the pieces and look for what I can use, and firmly make a decision to do better next time, or change direction to a more positive place. It is all about seeking the positive, for me. If I didn't look for the good I would spiral downward focusing on the bad.
I turn it into sadness or frustration then occasionally deeper frustration.
Disappointment is people related with me, either disappointment in myself or others. Perhaps from unrealistic expectations on my part. These days my disappointments are very minor, I have sadness in my life, friends, rellies, pets that are dying so disappointment is not a major concern.
I try to look at it objectively. Could I have avoided the problem if I'd done things differently, or is there something I can do now to make sure it doesn't happen again?
Do I need to make some changes, such as defriending or blocking someone, moving on from a relationship, changing jobs, changing website hang outs, etc.?
If it's not worth the effort, I just go for a walk, or watch Netflix.
I get over disappointment in a snap. I don't take things to heart. I don't carry a grudge. I start each day like it is a clean slate with new opportunities, yesterday is gone. Grief is the only disappointment that I have a hard time dealing with. When people I love die. That always take a toll on me. It is the source of my depression.