They know.
How do I know? Because I've seen them at work.
Just one example. Going back to abusive ex for a visit with DC1, he has my photo up in a frame (ah, bless he still thinks about me) 
Left, needed a wee, knocked on the door, go up to toilet, photo frame is gone? Checked the unit it was on, he'd put it back in the cupboard.
So he knows what he's doing. In the same way he cried and begged for me to come back, it's all an act.
I caught my parents talking about my brother (they are both narcissistic parents) and they were saying 'no no, you can't say that, you need to be careful with him, he'll cut us off'
So they know their actions have results/consequences.
They lack empathy, they are dangerous, they will suck the life and soul out of you, and they do not deserve your empathy.
They targeted you BECAUSE you have empathy. Because then it's easy to feel sorry for them.