You know, at first it was about money and power. From a Korean perspective, that belief is foistered on you early by your parents who believe that's all there is to life.
However, I found my own mentors and they taught me the thrill of doing medicine for the sake of medicine. I hope one day to become successful enough in my work that I would be able to do charity cases as well without folding under bankruptcy.. I could live very well off of 100,000 a year and really have no desire to earn more (until I have kids who have to go to college, then I'll probably rob banks).