What is the difference between a narcissist’s need for validation or just a person with low self esteem?

A narcissist does it only cause they think too highly and selfishly of themself like my disgusting sister. However one with a low self esteem does not feel good about themself and is a good person still like me.

Also one with low self esteem is not going to seek attention whereas a narcissist will. 

A narcissist acts on getting the attention they want, somebody with low self esteem is more likely to shut themselves out of opportunity, because they allow bad life experiences to keep them down, rather than using those experiences as a reason to get up and try again. People with low self esteem might want more attention, but many might not believe they deserve it. A narcissist outright will think they deserve it, at no cost to themselves, and again will go looking for it, manipulating situations, turning people against each other, making sure all that pity is only aimed at one person, themselves. If you've ever been in a relationship with a pity hungry narcissist, a sociopath, or a psychopath, you'll know what a horrible relationship is. It gets much worse than being "cheated on". <--- Which is as bad as most people have it.