I was once seeing a psychotherapist and during the appointment he got up to go to the loo. As he went out he said "it's very unprofessional of me, tb, but your mother is a complete bitch".
As he hadn't seen her - narc go to a psychotherapist? - he said he couldn't be definite, but he thought she had either npd or bpd - or both 
I think maybe that many of us - unless we've been in therapy, or done a lot of reading won't have heard of npd or bpd and will have ended up thinking that x,y,z is a complete bitch bastard etc
Don't know about anyone else, but I have a complete gap between what I know and what I feel. For instance, I have a report from Career Analysts that gives details of various sorts of intelligence from tests I did, I "know" it's true, but do I feel it? Do I heck as like.
I've often felt if I could only find the book that would explain things, I'd 'feel' better iyswim. That's also been true about the sexual abuse I've suffered.
I think it's something to do with being treated as expendable, or that if you as a person don't matter that is so horrid.
Another thing I can't decide - bit philosophical perhaps - which is worse - thoughful nastiness or thoughtless nastiness?
Thoughtful - done deliberately to you as a person, but at least they've thought about it
Thoughtless - done deliberately to you, but not as a person as the fact you are a person hasn't even come on to their radar.