This is a submission in a series of posts on interpersonally destructive personality disorders.
If some of this comes across as excessive, there is actually a healthy reason behind it. Because I am fortunately not fueled by resentments but rather by fascination, and a bit of obsession, with how each and everyone of us manages to maintain positive feelings towards ourselves in the face of unfavorable self-comparisons, failures or even abuse.
How this system works and self-regulates, to me, is a marvel of evolution, even if it is comparatively much simpler than many other systems its effects have enormous consequences to our happiness. So this is not only about educating others on the perils of dominating and abusive people but also is self-serving because I too can learn from it.
Nuts and Bolts of NPD
What I just mentioned above – self-esteem regulation – actually is the dysfunction behind someone with narcissism. It’s not so much about the addiction to wanting to feel more important than the rest or the romanticizing about how everyone will envy you when you have that perfect beach-front property and so forth. It’s about the need to suppress feelings of shame and inferiority that theoretically drive a narcissist to behave the way they do.
The most concise way I’ve seen the causes of narcissism put is as seen below taken from “The Self-Conscious Emotions”. This means that narcissists – we can all do this but again its a matter of degree – over time have become very good at getting defensive and inflating themselves when they feel threatened so much so that it becomes a feature of their personality.
Chronic experiences with certain self-conscious emotions can, in turn, shape people’s explicit self-esteem such that it differs in valence from their implicit selfesteem. In the context of the resulting fragile self system, narcissistic—that is, defensively self-aggrandizing—personality tendencies take root. 
To illustrate the unstable self-esteem, with one possible scenario, the narcissist could sense a “put down”, priming the mind to send a burst of shame as a warning to take heed that their sense of ‘self’ is in jeopardy of being tarnished. The defensive system then becomes engaged, and the narcissist focuses on the potential “threat to self” by getting defensive, angry and even inflating with hubris, anything but to feel the shame. And they have lots of practice at doing this because most theories posit that this starts in early childhood.
Shame, the output of a much larger self-esteem system, is what’s known as a ‘self-conscious’ emotion in that it works when you perceive that you are unattractive and undesired to others. To get perspective, imagine self-esteem as being something that encourages us to strive for status and acceptance by rewarding us with positive feelings (pride) upon meeting standards. But can, arguably even more so, motivate us towards self-improvement, or conversely to conceal defects and not compete, by the prospect of being punished with aversive feelings (shame) if we fall short of standards. But shame’s role only works well when we “care what others think”.
Shame emerges from our complex evolved abilities to be aware of “how we exist for others,” and make predictions of what they think and feel about us. 
The Ego in NPD
And it pays to “care what others think” at least it did for our ancestors in our distant past which aided them in figuring out how to be valued by others and to compete for resources and mates. For those that did not have this quality of insight may have been destined to becoming “not enough” and at risk for being exploited or even ousted by their tribe.
But this facet of us, the ego, has a dark side too since the very act of imagining “not being enough” is quite taxing to the mind and body. As much effort now a days is spent practicing how to quiet that nagging voice through mindfulness meditation and being more aware.
Ego is the one affliction we all have in common. Because of our understandable efforts to be bigger, better, smarter, stronger, richer, or more attractive, we are shadowed by a nagging sense of weariness and self-doubt.
This ego, which is colloquial for us for describing the turmoil of the self-conscious emotions, the yin and yang of struggles – to be dismissed or to be recognized or be laughed at or to be taken seriously – must be ubiquitous. In fact, I imagine the ego plays a bigger role than we admit to since our daily battles with it make us feel small if others knew that we were driven by such petty stuff, so its effects remain largely hidden.
In fact, self-conscious emotions play a central role in motivating and regulating almost all of people’s thoughts, feelings, and behaviors. Most people spend a great deal of time avoiding social approbation, a strong elicitor of shame and embarrassment. We worry about losing social status in the eyes of others and, as Goffman noted, our every social act is influenced by even the slight chance of public shame or loss of “face.” In fact, according to the “Cooley–Scheff conjecture,” we are “virtually always in a state of either pride or shame”. 
And so the ego is quite vexing, but the narcissist, the disorder not the person, has a simple solution to this problem which is to block the part that hurts and which keeps us humble but at the cost of others witnessing it grow without bound.
 Epstein, Mark. Advice Not Given. Penguin Publishing Group.
 Gilbert, Paul. Genes on the Couch. Taylor and Francis.
 Leary, Mark. The Curse of the Self: Self-Awareness, Egotism, and the Quality of Human Life.
 Leary, Mark. Interpersonal Rejection. Kindle Edition.
 Quartz, Steven. Cool. Farrar, Straus and Giroux.
 Tracy, Jessica. The Self-Conscious Emotions . Guilford Publications.