I was an athletic trainer in high school; interested in being a physical therapist when I went to college; ended up a long ways from either one. I finally figured out what these original desires had in common - I want to help people. Not particularly because I'm selfless and desire to further humankind or anything really sappy like that. The desire is more along the lines of being able to fix things. Broken leg? You get a splint. Short of breath? You get oxygen. Surgery on your leg? A routine of strengthening and stretching for you. All better, buh bye.
My current job has some aspects of this fix-it mentality, but ultimately is too far upstream from helping people. I can help with research, and maybe some of it will eventually change medical diagnosis, treatment, or policy. But the day-to-day aspect is that I'm furthering the research careers of individuals who frequently express their motivation more in terms of publications and their relative position to other researchers than in terms of making a difference. Everything is tentative, needs additional follow-up studies, and will never be the final word. Otherwise, there wouldn't be anything to ask for more grant money to do, or write more papers about.
I consider my position almost strictly service-oriented. People bring projects and I produce results. It is both the secret to my success and the torment of my days. I'm ready to try a more direct method of helping people. One of my long-held fears about this sort of thing is that I don't want to listen to people complain, and complain, and complain. What if I don't want to help them because they're too annoying? Maybe I'm mellowing with age, but I finally feel like that won't be a problem, or at least not too big of a problem. I've been trying out this new field in a limited way and even "teenage girl syndrome" wasn't as bad as I feared and most people don't want to be a bother, even if they need help. I've spent a lot more time trying to convince people they need help than vice versa.