Object relationers sound really corny when they say “Narcissistically dysfunctional people don't believe in love”.
Then Freudian come in and say “They need to camouflage.” without explaining why wouldn't they just be their normally selfish self to save the work.
Then medical people come in with behavior checklist pages in the DSM and tell you “shame” is the origin of their disorder.
But why does one thing have to do with another?
Being human means imperfection. But when someone can't accept half of themselves, they can't accept that in another person. So when they are alone they might think once someone suitable comes around, they will treat that person well, and they really mean it at that moment.
But any attempt to get close to another person will face with the reality that the person they have found, is, in fact, not perfect. And attempt to resolve that reality, either accept that they made a wrong initial judgment, or that they are not that warm or generous toward someone else as they have hoped, or that they have the weakness to be dependent on another person,... is a proof, that, they themselves, in fact, not perfect.
That triggers shame. And what do you do when you feel shame? You try to prove that everyone else is wrong. There comes camouflaging.
That's why the opposite of narcissism is not kindness, or generosity. It's about not accepting easy sets of answers from someone else but finding the answers yourself.