Yes, it sure does, Anjae.
The human mind is very complex and there is so much we still don't know.
Milly, I agree with what you said. There is just something missing with a true Narc.
"I don't believe my sister ever has a day when she's genuinely a good person. She is only apparently 'nice' because she's after something."
I found this to be true with my 1st H too but not until he got into his early 20's, that I recall. If being nice served some purpose for him, he could do it.
There are documented cases of children who are just born bad. They never reach the level of any kind of human feelings. Doctors don't have any name for it, they just call them "toxic" kids. No real explanation for them to be that way. Their parents could be wonderful parents.
They can become very dangerous kids who harm their parents and siblings with no apparent feelings of guilt or empathy.
To date there is no cure or medication for these kids. They usually end up institutionalized because they are dangerous.
I still remember my 2 year old son sitting in a high chair and my H calling him a bastard. Only because he needed my attention.
Sick stuff.