I'm sure the thread already exists somewhere but I couldn't find it.
Seen all sorts of speculation about HPD being a female version of NPD, or a cross between BPD and NPD etc.
Most important/specific answers I think?
Classic NPD:
"Look at me, help me prove to myself I am worth more than others, give me the means to construct/inflate my ego and hide from myself that I have none."
"Typical" HPD:
"Daddy Daddy!(or mommy) - Look at meeeee! Love meee, please? Am I getting your attention yet? Please love me."
I could elaborate loads, but I've got a feeling the rest has been discussed already. Just never seen the basic motivations behind them written here! - (Or maybe missed them.)