It's an extension of my wanting to control things, I think, and my wanting to manage all of the unpleasantness in my world. It's hard for me to enjoy my own feeling-good-ness if anyone around me is feeling less than good. So I take on everyone's stuff. I want to carry it so that they don't have to, as if I can do that and still enjoy myself.... But that, of course, is not true, so instead of relieving other people, when I take on their stuff as my own to bear, they don't feel any better, and neither do I.
I suppose, if I look at it the right way, it's got to be ok to feel great when I feel great, because the truth is that feeling great doesn't last... not for any of us. The truth is that we all have our turn in the barrel.
It's not my job to fix other people. Life is about sharing the ups and downs that we all experience.