I answered a similar question with:
“Curiosity. I always want to know why things work and how they work. Science seemed like the best way to do that. It was interesting at school and you got to do experiments which were more fun than sitting reading books or writing stuff.”
Also some of the science teachers at my high school were really good and made it really interesting – its easier to be interested in something when the people teaching it are enthusiastic and make it fun.