I couldn't agree more on the passion thing. Last year at school, I absolutely loved science (especially geology) and I kind of started to like maths after 3 years of having hated it with all my heart. I got good marks for it and for once I actually felt like I was learning something. But now, I can't stand either one of them. Not only do I not get any good marks anymore, but it has either become so boring that all I can do is stare at the clock and wait for it to be over, or it has become so stressful that it's a miracle I didn't explode out of rage in the middle of class.