Early in life I learned to deal with being disappointed. But, it wasn't until much later that I learned to master disappointing others. For a well-behaved, intelligent overachiever, giving people what they want, sucking up, and doing really whatever they tell you to do can become nearly automatic. It wasn't a question of whether or not I'd do well on a project; I'd just put in the effort until I was assured a good grade. It became a neverending cycle that kept me craving approval like a little Lisa Simpson.
It didn't really stop until sometime in college. Studying really hard in a class I hated and just didn't get (Differential Equations) and then getting a 34% on the first test was a nice rude awakening, though also an experience that none of the rest of college ever really lived up to. What really did it, though, was finally realizing while answering tech support questions for my software, that nothing I could do would please everyone. Some design decisions in my software were mutually exclusive; I could make one person happy or the other, but not both. Some peoples' demands were just unrealistic. I could have worked full-time on all of my software, and someone would complain that I should have worked on something else. Nothing would satiate these people. And I think that's when it really hit me: I didn't have to. I didn't have to make these people happy. Sure, I like making people happy; why else would I spend so much of my free time offering free support for free software?
I learned to accept that some people I would make extremely happy and they would love me forever, and some people wouldn't get the answer they wanted and would be very unhappy. It wasn't my fault. They were just going to be disappointed. I learned to just be pleased with what I'd done, and not displeased when not everyone was happy about it. And that's a very important lesson to learn.
I think there are people who need to learn the opposite lessons too—some need to learn to deal with being disappointed, and some need to learn how to not disappoint others. All three are important skills.