I was stuck at a startup for 7 years. One of my coworkers told me on my second day of employment that I almost didn't get the job because they were afraid I "wouldn't fit in". They were right, and did multiple things to make sure that was the case -- set up my desk alone in a separate room away from the other 5 engineers, frat-boy humor... I tried advancing to management but got no support and demoted myself in a matter of weeks. I eventually landed my own office in a 5x8 room so I didn't have to deal with anyone else there and did minimal work for the rest of my tenure. I stayed as long as I did for stock options and the promise of going public (we never did). I cried in my office behind my door on many occasions over 4 years and was too beaten down and lacked any confidence to get a new job. Couldn't take another day there, but also couldn't survive without it.
I spent a year in therapy to try to get some sense of confidence back. It worked to some degree but the saving grace was a former co-worker offering me a slot at another (large) company as he was building a new team with a bunch of other former co-workers. It was exactly the sort of known-quantity that I needed to start over again without having to prove myself to a bunch of strangers. That job didn't pan out so well either -- the new team collapsed in a matter of months but I was able to tread water for a couple of years until I got my current job.
I'm back in therapy for different reasons but I'm comfortably employed again. I blocked the key actors from the startup but the whole experience still hurts, even 15 years later.
I know this will pale in comparison to what others will post here, but it's my story.