It's all based on intrinsic and extrinsic motivation, you either want to do it and motivate your self, or you let money or prestige motivate you. I will say that even some of the most respected docs did not bust their @$$ to go to med school just so that they could help people. A lot of the motivation comes from money and high status. Then again there might be some people who say 80 hour work weeks and 260k debt is worth it because they like to "help" people. I honestly think people use "helping others" to cover up their other extrinsic motivations. Why wouldn't they when med school look for people like that?