Or say you got the perfect job and some of your friends hate theirs, they are doing nothing that they went to school for. You cannot be too excited when you tell them, if you care about their feelings at all.
Or maybe you are trying to get fit. You are working out and eating right, no diets or gimmicks. You have lost some weight, but every single person that you want to tell, has not had the same success as you. You want to shout it from the roof tops, but really most people would just hate you and not want to talk to you. It would be counter productive. I felt that way today, for a week I have worked out and ate reasonably well and I have lost three pounds, but today I did not feel as though I could tell anyone because I did not want to be pushing it in their faces.
The reality is that most people are not happy for you when your life is going well, or maybe even one area is going well. They do not want to hear it, if their life is not. It is true misery does love company.
Sorry to be cynical, but their are a few people that will be happy regardless, and these people care more about you than they do about themselves! These people are real treasures, keep em close!