I think we don't even realise the impact we can have on people, deliberate or otherwise. Years ago, when I finished highschool, this guy came up to me and said "thanks for acting normal to me, it really helped me through the last four years". I kinda knew he got bullied, but I never really realized how much it bothered him or how my interaction with him affected him. He was just this guy, and on occasion I'd talk to him if I saw him in the hallways.

Since then, I've always had the feeling that you don't really have to try hard to have a meaningful impact on other people's lives. Just be nice in general and you'll have more impact than you can imagine.