I think their internal perceptions are so flawed that they percieve themselves to be more defective than they really are, mistaking universal human frailities as their uniquely terrifying cross to bear.
And the one overriding flaw that they can't or won't deal with, their lack of empathy is the one that allows them to turn what would ordinarily be just some unpleasant traits into the puppet show from hell they try to create around themselves, in order to insulate themselves, at any cost to others, from what they think reality will do to them.
Mud, the first sentence could be applied to some of us, also (like myself). But instead of demonstrating lack of empathy toward others... I turned that laser-gun of self-perception distortion on myself... and perhaps had some help in doing so, you know? (projection)
Do you think perhaps, that the puppetry becomes a self-validation in NPD? In that - by exercising "power" (or the illusion of it) over others, some of that fear of being revealed as "less than human" is calmed? That the "payoff" for the constant campaign of control, meanness, etc is simply a way to reassure themselves that what they're afraid of - is manageable? That this is how they've coped with a need for a feeling of "safety"?
That still leaves open the question of whether or not, Ns or NPDs are capable of changing. As much research as we've collectively done here, I don't recall much in the way of stories of successful treatment. Perhaps - and I'm going way out on a limb here making a lot of assumptions - perhaps the suggestion to remove NPD from the DSM is a way to acknowledge the fact that these people are not treatable?
My Dad - the classic N - could fire all his employees on a whim (and did). But he also went out of his way to help others, too. He was capable of apologizing and admitting he was wrong. He was able to change himself and his behavior over time (until his stroke). My mom on the other hand - is exactly the same as she was when I was growing up... is quite content in that... and it's the rest of the world that's stupid, wrong, and rediculous - not her. And she's quite incapable of self-awareness - of understanding how what she says and does affects others.
The one thing I would add to the consistent traits list, along with lack of empathy is that
lack of self-awareness, too. Specifically, the lack of self awareness of how they are really seen by and awareness of impact they have on others... followed by the lack of empathy. I've seen this in both N-ex-husbands; my mom; my old Nboss.