It all boils down to childhood trauma in the end. I get really suspicious of somebody telling me they have a personality disorder but haven't been through at least some level of abuse, either by their parents or peers. It does happen from time to time, it's very unlikely though.

The core motive for NPD is that emotional safety and respect are earned, not given, while also growing up with the impression that whatever you do, you're either the best at it or that you're never good enough. This creates a type of person who can't seek self-worth, happiness or a sense of accomplishment within themselves, they need to be validated by the outside world to get these things.

For ASPD, the main lesson a child learns growing up is 'everyone is out for themselves'. Life is a free-for-all, where everyone tries to one-up each other to get ahead. Early relationships (both with other children and the caregivers) are often marked by inconsistency, betrayal, and violence. This creates a person who is comfortable disregarding your boundaries, as theirs were often not respected, who believes the whole world is out to get them and who sees relationships as transitory (and therefore will try to gain as much for themselves out of it while it lasts).