I was laid off from my welding job. My boss liked me, so he helped me get a job at another shop. But I was in a really bad head-space in that time of my life in general, so that combined with a few other things, and I quit that new job within about 2 days after starting.
I was totally unable to find a welding job after that. There was a reason the first so laid me off after all - oil markets had crashed, and I lived in a very oil-dependant city. So I ended up working temp jobs to get by, but for a solid 2 years I did nothing but kick myself for being so stupid. To this day, I think quitting that job was one of the stupidest things I've ever done.
Anyway, after 2 years of that, I finally decided to change gears entirely. I went to school, got a CS degree, and now I have a cushy, well paying programming job.
I still think it was stupid to quit that job back then, but if I hadn't, I wouldn't be where I am now. I often think about how I can apply that way of thinking to other areas of my life.