To be only capable of loving yourself at a exaggerating level.
Narcissism ruins lives and is one of the main reasons this world has problems.
People who are a narcissist think very highly of themselves with no reason or proof at all.
They are almost always arrogant, egotistical, manipulative, have little to no empathy and have a desire to control the people closest to them.
When feeling personally attacked they will react very recklessly or very tactical on the current situation, no matter who or what will suffer the consequences.
Most relationships (especially the people closest to them like: partner, parent, child) will become very toxic over time.
When that happens the narcissist will always blame them for their "mistakes" en try to make them believe they are the bad person by almost any means neccesary like telling carefully constructed lies with fake proof or by manipulating the third party.
This can cause emotional issues to the victims that can follow up with other mental problems like depression or even narcissism itself.
The worst thing is that they are AWARE of their behaviour.
The best thing to do is to leave them. When that is not possible go talk with the people you trust and/or seek help and information about them.
When engaged in a discussion with one, try to trap the creature with proven truth, especially in front of honest people or let it "bump it's head" in the near future.
Never. Let. These. People. Get. To. You.
Narcissism in a nutshell:
Narcissist: It's me, myself and I.