There have been numerous psychological studies done on human children to see if empathy is something we're taught or if it's ingrained. The general consensus is that it's a combination of both nature and nurture, but that by the age of 9 months most children are capable of showing empathy to another human being.
When it comes to narcissists there are a ton of theories on why these people are empathy deficient. Personally I think a combination of things make up a narcissist, but whatever it is that makes them the way they are makes it very difficult to try to understand why someone else would be hurting, or upset, or feeling used. Anger they can understand, but those more subtle emotions are really beyond their ability to recognize. Enter into this a person who's extremely empathetic...they get when a person is hurting or upset or feeling used. They instinctively try to make that other person feel better. The narcissist will jump all over this person because this person gives their attention to them freely, at least in the beginning. In a normal relationship (which is what the empathetic person is used to) there is a give and take. An exchange happens in a normal, healthy relationship (whether it's a friendship or a romance) so that each person receives support and feels like they are appreciated. Unfortunately, when one person in a relationship is a narcissist, the relationship becomes a vacuum with the narcissist constantly pulling from the other person.
The great thing about the comment that started this little post is that saying 'it feels like manipulation to appeal to a narcissist's needs' shows that the person making that comment is very high in empathy. Because if you're worried that you're hurting them, then you're feeling something a true narcissist can't.
The other thing I wanted to mention is how invested in the relationship the narcissist is. I haven't seen this discussed much, and have only my own experience with my mother-in-law Narcissist to go by, so take this with a grain of salt. The example in the video is of someone going to talk to their boss, who is a narcissist. In this example the narcissist has an investment in the relationship, but it isn't an emotional investment so negotiating both parties' needs might be relatively easy.
So my big take away from this whole thing is - it's good to be empathetic, but you've also got to watch out for yourself. Self care means stepping back from relationships that leave you feeling drained or vacuumed out. It really is okay to say no, step back, and leave some people to fend for themselves. Sometimes as an INFJ and HSP this can be difficult, but not stepping back is worse.