People typically limit themselves when it comes to taking advantage of others because of a little thing called values.
Since the narcissist doesn’t have the empathy to truly possess a value system and is simply faking it, there is no limit to how far they’ll go to exploit and use others. They only care about achieving personal gain, whether it be financially, emotionally or psychologically.
Think of narcissists working on others like an incubus does.
They’re attacking them in a psychologically or emotionally dormant state, depleting people of their energy and positive, humanistic traits and then leaving them wholly dependent so they can continue to utilize them for personal gain for as long as they can.
Fuckboys are not this methodical.
Although they do and say things that are not generally praised by the general population, they only do so because people let them get away with it. This happens consistently enough for them to think it’ll continue to work.
That way, they think they’ll be able to achieve whatever they say they will.