The reasons of failure vary from person to person and most of the time these factors play the demonic role in one’s failure (as bro srk345 previously mentioned):
1) Bad Luck
2) Lack of confidence
3) weak English
4) lack of writing practice
5) over confidence and poor time management
6) opting out for wrong optional
7) poor selection of essay topic.
8) too much reliance on notes
9) Lack of commitment
10) procrastination

But the most important of all of these is the luck factor. I sat in CSS for the first time in CSS-2011. My papers went very well and I was quite hopeful of my result, but the result shocked me as my name was nowhere in the list of passed candidates. I couldn’t express the pain and the dejection I felt at that time. Furthermore, I was shocked when I saw my DMC, I had secured 733 marks in CSS but I was declared fail because I got only 36 marks in English Essay paper. Yet I didn’t lose heart and started preparing for my next attempt with full throttle and now I have Alhamdolillah passed in CSS-2012’s written attempt. What I want to tell you is that all of you should not lose hope. Had I lost hope after CSS-2011 failure, I would have never passed in this second attempt. So it’s my humble request to all of you is to forget about your failure as failure is the stepping stone towards victory and study well so that you pass in the next attempt inshaAllah!

Precautionary Measure:
I will not advise those who get less than 650 marks overall in Punjab and 615 marks in other provinces to sit in CSS-2013 if their age and household situation permits them to sit in 2014 or later.