Actually I found it very difficult to understand how it had happened. At school I was one of the best, I enjoyed maths, I understood the concepts and mostly found it easy. At University that all reversed: I was one of the worst, I couldn't do the assignments, I found the lectures boring, and I thoroughly disliked it. I found it very hard to comprehend how such a complete reversal had happened. And more than 15 years later, I still don't really get it... It's rather destabilising when you can't do the thing you expected to devote three years of your life to!