I'll start. I have to be careful drinking around other people, because I can get intensely motivational.
My neighbour used to be depressed and stayed at a cruddy job, despite poor pay. I was 17, and he was in his 40s. Well, one night we happened to drink together. It turned out he only stayed at that job in hopes that he would eventually get his parents approval, and that they would finally be proud of him. The job made him miserable.
I spent hours convincing him that he was worth more than his parent's approval, and that he deserved to be happy. That he was the one living his day-to-day life, and that he should live it how he wants to. Many tears were shed that night. Dude quit before getting any new job prospects, and ended up working in a completely different field. He said thank you more than a few times, after everything was said and done.
That might not sound bad, but it was far from a one-off scenario. I eventually started to wonder what would happen if I accidentally helped lead someone to make a bad decision. It's not like drunk people are known for making good decisions. So, I only drink around certain people now haha.
On a side note, a crazy number of people have problems with/from their parents.
I knew a guy who was a very outspoken but peaceful vegan, didn't want to harm anything. Animal rights activist. Super nice guy, when sober.
But he also had a drinking problem, and totally flipped when he drank, you could almost see the switch happen in a few seconds when he was at 4-5 beers. His drunk personality was angry, paranoid, quarreling and violent, and he would often get blackout drunk and get into fights and whatnot. Got himself banned from several bars.
I didn't know him well, but he probably had some trauma/bad shit in his life. He never talked about his family, except his grandmother who apparently had raised him, more or less.