Staying at my previous job too long. 9 years. At 5 years it started to turn toxic. I always hoped it would get better but it didn’t. I should have left sooner but I wanted to finish the project I was on because I wanted to leave behind something to feel proud of. In the end the company screwed my over. But I have a better job now so it worked out ok.
Of course, it wasn't. I've been out over a year now and getting into a position to be able to walk away financially and then doing it was one of the best decisions.
I'm hoping the lessons I've learned balance out the psychological damage I took pushing through burnout for three years.