1 They got hurt
If a Narcissist got hurt or if they believed that they got mistreated then there is a high possibility that they will block you. Narcissists cut connections immediately with the ones who hurt them in order to feel good.
2 It's a form of Devaluation
When a Narcissist gets mistreated by someone they might devalue them. Devaluation is the act of considering the one who hurt them worthless in order to feel good about themselves. For a Narcissist blocking is considered one form of devaluation. See why Narcissists devalue you.
3 To make you feel worthless
Narcissists sometimes attack people's Egos in order to feel good. Narcissists do that to the ones who hurt them or disrespect them. In such a case the Narcissist might block the person who hurt them in order to make them feel worthless.
4 Perceived Mistreatment
A Narcissist might block someone all of a sudden even if this person did nothing just because the Narcissist believed that this person intended to miss treat them. In such a case it's the wrong perception of the Narcissist that results in such an action.
5 You ignored them
Narcissists might feel like blocking someone if they believed that this person is ignoring them on intention. A Narcissist could block someone who didn't wish them happy birthday if they believed they did it intentionally.
6 They decided to cut connections
When a Narcissist blocks someone it usually means that they took a final decision to cut connections with that person. This doesn't mean that the connection will never be restored for the Narcissist can change their mind later if they got the treatment they wished to get.
7 To send you an indirect message
When Narcissists block people they want them to know that they did it. Narcissists do that to send people an indirect message telling them that they don't mean anything to them.
8 To Manipulate you
Sometimes a Narcissist blocks a person because they don't want to comply with their rules. I such a case blocking that person can be one form of putting pressure on the person in order to comply.