Surely we shouldn't impact on others? I mean, who am I to make any impact/have any effect on someone else's life? It's not my place, surely?
We should avoid negative impact, but positive impact is... positive. A former colleague contacted me recently, to say thanks for the training I'd given while he was here, because it helped him get his new job. (Which, ironically, I would never have gone for, because I would have said I don't have enough knowledge, which probably says something about my own self-esteem...)
That's quite a different sort of impact than of he'd left thinking, "she never helped when I asked, she gave us loads of work without discussion, then shouted when we didn't finish quickly..." We all have some sort of impact on people, unless we are total hermits, and it can be a very good thing.
Self-esteem is s tricky thing, though. There are technical, procedural things I'm really good at, but if I get feedback about things like how I relate to others, how others see me, the things they associate with me - it's not usually my technical abilities, but how I stand up and speak when I think things aren't right and push to get improvements made. My initial reaction to this sort of feedback is usually, oh, you're just saying that, you're just being nice, you're going to ask me to do something. It's hard to accept it when part of you doesn't believe it, even if rationally, you know they've got a point, and they're not after anything.
I don't totally know what the answer is. But I do know that having a positive impact on others is a good thing - but it's also good to do things for yourself. Feedback from others is nice, but your self esteem shouldn't rely on it, and nor should your sense of self-worth be based solely on doing things for others, which I think women can be prone to. Sometimes, you need to do things for yourself just because you want to and you enjoy it.