A useful post from Tim Ferriss on learning, service, and karma:
Service isn’t limited to saving lives or the environment. It can also improve life. If you are a musician and put a smile on the faces of thousands or millions, I view that as service. If you are a mentor and change the life of one child for the better, the world has been improved. Improving the quality of life in the world is in no fashion inferior to adding more lives.
Service is an attitude.