What do you want to be when you grow up?

Kids are asked this question rather often, and would usually switch their theme once in a while, but a profession that seem attractive and prestigious to us, their parents, would not always seem as much appealing to them. My son was convinced that I worked on the train since before we had a second car dad and him would drop me off at the metro on their way to pre-school, saying that mommy is going to work and everyday on their way back they would pick me up from the metro saying that mommy is back from work. He was really proud and was wondering whether I drive the train or monitor the people going in and out. He was very disappointed when he found out I was just a scientist. He says that when he grows up he wants to be either an astronaut, a soccer player or a helper. I asked what kind of job "a helper" was and he explained that a helper is someone who's job is to help others. Sounds like a broad range of professions, so I asked for an example and he said: "a superhero". But even after you grow up and make your choices, things are not always as clear as they seem when you are a child.
I love science and enjoy taking part in the medical research, but as a graduate student and even as a postdoctoral fellow I always wondered what drives a lab chief or an assistant professor to devote their lives to research? And usually to a very specific field of research. What is their source of motivation, that keeps them so focused on this one thing till the end of their days without looking back? And they usually don't look back.
The day I found my own answers to those questions was the day I made my promise. When my daughter looked at me with desperate eyes asking if her diabetes will ever go away, I just couldn't let her down and said: "yes, when someone finds a cure". She asked how long it would take and I said it will probably take years and that was my most optimistic projection. For her it seemed too long. "But mommy you are a scientist" she said excited. "So go back to work and find me a cure!" And so I made my promise, not totally clear what it would take. But by that I discovered my drive, my motivation and my professional decision. I am not the first scientist to switch her field of interest from these kind of personal reasons and am surly not last. I left my lab and my neuroscience research to a lab deeply focused on type 1 diabetes research and have a smile on my face every morning when I come to work, knowing I no longer have to be helpless in the face of my daughter's diabetes. I am doing the most that I can to change it, I no longer need to look back.