They might have been raised by both a dominant and a submissive parent/ caregiver
They see the dominant person as powerful and a submissive person as weak.
They might think that the powerful person cannot feel pain and that the submissive person can as they witness the unbreakable powerful person control the submissive person over and over.
The Narcissist as a child will either subconsciously absorb the behaviour of their Narcissistic parent or the submissive parent. If it’s the Narcissist traits they are absorbing more then subconsciously they never want to experience that powerless feeling again so they take on the behaviours into their teenage years and so it begins and they’re in defense mode permanently (I hope this isn’t true. I’m still hopeful that there are narcs in recovery)
Their past is so painful that they would rather feel like the one with the most power over anyone.
They realise it’s not appropriate to behave like that in every situation so they find an empath who has a good heart and sees the good in people making them easier to manipulate because their goals are to help people and put other’s needs before their own even if that means having the soul drained out of them. The empath may have low self esteem and reminds them of their submissive caregiver who became open to it making that situation something that they can get away with in secret.
That’s my perception on it based on my experience and what the Narcissist told me—that everyone was mean to him and how I’m not like that, so I tried to live up to that while the bond was being made. Once I was sucked in he told me I was changing into this selfish person because I wanted to spend time with my friends, which was nothing new.