Hi Gratitude,
I do think abuse, bullying, are the prime causes. And I'm no expert, but I personally believe there's a genetic trait as well that encourages it.
Plus, there's also taught N-behavior, so if you sibs were around Ngrandparents who made an impression, I thought that might be a partial explanation.
Also, if there are such things as demure or passive-seeming Ns, perhaps one of your parents has it in a less visible way?
I remember once reading profiles of alcoholic behavior and one example given was excessive-repressive religiosity, and the authors said there are circumstances like that that can create alcoholic personalities even among teetollers...really caught my attention because my parents never drank at all when I was young, yet Mom is surely N.
So maybe there are some forces like that that cause Ntendencies, too?
Hops