> I came across narcissism. The idea that you’re smarter than everyone else. Comes from a grandiose sense of self importance.
This may be the colloquial description of how narcissism manifests, but it isn't even close to (and possibly completely opposite) clinical narcissism. The grandiosity isn't so much a belief as it is a "false self" put on to garner caretaking from others. It's not "I got all the toys as a kid, so I deserve more stuff!" but a failure to individuate from caregivers. "Mom (as a tool, not a wholly independent person) came when I cried as a kid, so I need you to lavish attention on me and make me feel better now as an adult. I can't see myself without external input; I only see myself as a reflection through you."
Disclaimer: I'm just an...interested layman, but as far as I know we don't really know. It looks like there's both genetic and environmental components to it; your genes have a big impact on your "temperament" and more volatile temperaments correlate more strongly with cluster B disorders. But it seems like neglect, a failure to recognize a child as their own independent person (basically "my needs are your needs"), from parents/caregivers who are often themselves narcissists contributes pretty strongly, too.
The Little Shaman[1] has been one of the most comprehensive-yet-approachable resources I've found for understanding these kinds of high-conflict personalities. In particular [2-4] are pretty relevant to your question.
This may be the colloquial description of how narcissism manifests, but it isn't even close to (and possibly completely opposite) clinical narcissism. The grandiosity isn't so much a belief as it is a "false self" put on to garner caretaking from others. It's not "I got all the toys as a kid, so I deserve more stuff!" but a failure to individuate from caregivers. "Mom (as a tool, not a wholly independent person) came when I cried as a kid, so I need you to lavish attention on me and make me feel better now as an adult. I can't see myself without external input; I only see myself as a reflection through you."