This took me back to the day when I was contemplating the same thing. Whether I should leave the safety and comfort of my well paying Engineering Job for something that I am not sure about.
I think you should consider your background before you make a decision. If you have people depending on your income, then it wouldn’t be wise to leave the job and keep them hanging. In my case that was not a pressing concern.
If you have a girl friend, then you should consult her before you make such a decision. I did, and I should say that was the most prudent decision I took at the time. She is my wife today. This is a decision that will impact both of you.
If you are not sure about yourself, take leave from work for some days and see if you still have it in you to study again. Sometimes the drudgery of daily work would compel you to look for greener pasture. It would only land you up in a similar situation even after you clear the CSE, only now you will have wasted the income that you could have earned for so many years.
Finally, be assured that there is no guarantee that you will clear this exam. Civil Service Exam is as much an exam of chance as it of hardwork. Anyone who is telling you otherwise is either too full of themselves or too shallow to comprehend reality. The only thing you can do is to work hard and smart and give it your best try.
Finally, let me just tell you how my decision to quit my job worked out for me. I cleared the exam in my third attempt. There were times when I thought I made a stupid decision; times when I thought I was not smart enough; times where I felt like the world was mocking me. However, somewhere deep down, I really knew that I had to do this now and I kept pushing against the wall. And guess what happened. That huge wall called UPSC gave way. The world became a happy place in one day, all the doubters became approvers, I was the smartest person ( as far as those around me are concerned) and life became a lot more colourful.
As far as I am concerned, I just became stronger as a person and was in harmony with who I am as a person underneath. So after due consideration of all the above things, you still feel that you should leave your job, then you should. There is only one person who can make that decision for you.
It is you.
All the Best.