Worst career/work-related mistakes you have committed
Just recently, I went for a job interview at the company I previously worked at. Having worked there before, I easily aced the exams and the interview. During the final process however, they found my old record and what they saw was a deal breaker for them. I had a feeling it would turn out that way but I still went anyway. Of course, I knew how I performed better than anyone and I sucked. Just before I resigned, I did not really care about my performance at all and just let my stats go down. I totally widthdrew myself from my boss and workmates and just disappeared once my resignation was approved.
Moral of the story, don't burn bridges, shut doors, or cut off connections even when you are leaving your job. As much as possible, leave the best impression you can because who knows, you might want or have to go back there someday or have to ask them for some favors. I learned my lesson and I learned it the hard way. You have been warned. Even when leaving, remember, keep those doors open.