I agree with the views of Gintino & Norymberskie.

My Analysis:
I scored 73 in Gender Studies with preparation of a day or two whereas I scored 30 in Psychology with the same one or two days preparation. I was expecting about 50 marks in Gender Studies but due to high scoring trend of this subject this year, i got 73 marks. On the other hand, I chose psychology due to its high scoring trend (till last year) and my interest in it. But when I saw the DMCs of PMS this year in which the sudden downfall of the scoring trend of psychology occured, I immediately perceived that if the same thing will happen in CSS this year then I would be fail in it because I could not perform good in the paper. Therefore, I would say that there is 40% role of your preparation (i.e. hard work + aptitude) and 60% of scoring trend (or luck) in your marks. So, I derived an equation:

40% * Preparation + 60% * Scoring trend = Your marks