i revised consistently, did past papers, went to every lesson, took good notes and was on track to get A* A* A*. I got ABB. As much as you revise, as much as you try, it can never EVER mean you'll get top grades, especially if you do 'essay' subjects (I did English, Classics, Theology). The marking is to some extent subjective. I felt confident with my subjects and never slacked through the year, and I got good results but by no means what I expected. It's just how it works out.