In my first year in medical school, we were learning basic sciences which was more or less an extension of stuff learnt in senior high. I felt I knew enough; I was doing so well in my tests and exams, so I decided to "chill"
Second year came and we started proper pre-clinical lectures. In other words, we started learning completely new stuff that I had no form of knowledge about. But I kept reminding myself that I was a really fast reader and I'd catch up with my peers early enough.
I was almost rounding up my third year when it hit me that I was just two months away from my first professional exam! I had two years worth of workload to cover in two months! I ended up passing the exam in one sitting, but the stress I had to go through was enough to change me.
I'm in fifth year now, and I've learnt my lesson. I do the things I should when I should.