I'm kind of this way also. My work motto was always: "Be the best worker and you'll always have a job." This was easy, because I was always curious about how things worked and didn't mind helping others. In my thirties, while training for a new position, I thanked my trainer for his help and he told me: "You seem willing to work and now I won't have to do your job for you." That simple statement changed how I thought about coworkers. Gradually, I became less helpful to the ones who thought it was a good idea for me to do their job with/for them.