I agree with Aniket who said parents who impose their failure on their children.
My parents were loners and didn't really have friends of their own. The genesis of this was that their parents (my grandparents) considered them their favorites in each of their families. My father and grandmother (his mother) were really mean to his sister because he was the prince in his family. We would go to my aunt's house, and my father and grandmother would expect her to wait on them. It was ugly. The situation was similar in my mother's family, with my mother being the princess of that family.
Consequently, people outside the extended family didn't enjoy being around my parents, and my parents didn't have friends of their own. Most of the extended family didn't like them either, but my father was the only person to go to college in either family and made more money, and it always seemed like they were intimidated and that's probably why they never spoke up.
My oldest sister got the brunt of my parents' abuse, especially from my mother. When she started kindergarten, my mother began to actively encourage her schoolmates to make fun of her. And this lasted years. My sister basically believed something was wrong with her and that she was somehow unlikable. My mother did the same thing to me but later, starting when I was about 9, so it did not affect me as much because I could see what was going on. My mother's behavior was motivated by her jealousy because she never had any friends of her own.
My older sister has been estranged from everyone for a couple of decades. There isn't closeness among the other siblings that are technically still talking to each other. While we were all growing up in that abusive environment, we were constantly throwing one another under the bus because none of us wanted to be the focus of either of our parents' rage. As a result, my other siblings and I don't have much of a family bond, and we just see each other once or twice per year, and it's fairly perfunctory.
For some reason, it wasn't until after my father died that it occurred to me that all these peripheral adults who were aware of what was going on when we were children did absolutely nothing. We went to a religious school, where they just reinforced lessons like, obey your parents, etc. there was one time that our family doctor told my mother off, one of the few times I saw someone actually challenge my mother. I'm thankful he did otherwise I would have thought I was crazy.