Personality can be understood as a kind of strategy or pragmatic functionalism.
This aspect of it can be conscious, semi-conscious, or non-conscious and is most common or apparent in social milieus.
Personality is a unifying principle or unifying group of principles and ideas that guides the individual in all settings.
Personality must also comport with the individual’s understanding of ethics, morals, philosophy, eschatology, and so forth.
While it may benefit me in some ways to lie, lying does not comport with my ethics so I won’t do it in most situations, though I may wander into or toward gray areas sometimes.
A major aspect of personality is how big that gray area is (if the individual perceives it at all) and how often it appears in real-world situations.
The dictates of culture, or cultural norms, are also standards that lie at the heart of how a person’s strategy for functioning in the world works.
In this context, narcissism or narcissistic behavior can be analyzed fairly simply.
A conscious narcissist is someone who uses the unifying principle of self-interest as a strategy or guide, often at the expense of sound ethics and fairness toward others.
A semi-conscious narcissist is one who does this in a more muddled way.
A non-conscious narcissist is one who does this out of training, lack of awareness, or cognitive decline due to substance abuse or injury.
The first kind—the conscious narcissist—can change easily if conditions are right. So can the second kind—the semi-conscious narcissist—though good conditions will be harder for them to find.
The third kind is less likely to change because the cause is organic. This kind illustrates the raw functionalism of personality. A simple principle such as relentless self-interest is easier to hold in the brain than a more complex one that factors in fairness and ethical standards.
Many other personality traits can be analyzed and understood as practical strategies that are used by the brain to guide the organism. In some cases, these strategies are complex with varying ties to ethics and fairness.
In other cases, these strategies are the simple standards that remain after organic damage in the brain has occurred. I am pretty sure this is one reason the Buddha made the fifth precept “refraining from irresponsible use of alcohol.”