Your walking down the street and someone says hello to you and so you say hello back and keep on walking. You most likely deemed this as a nice gesture, refreshing or an act of kindness, and your day goes on. Most people do not interpret human interaction as a tool to define oneself.
When it comes to the narcissist, they interpret every interaction they have as a means to fuel their false self, delusionally interpreting human interaction. The narcissist’s 24 hour focus is their false self, their only self.
The narcissist is delusional. Many believe that for a person to be delusional, they would need to be running down a street naked from UFOS but this is not true. To live your life constantly interpreting every external stimuli perceived as a mirrored reflection is not only delusional but extremely obsessive. Essentially, the narcissist is delusionally obsessed with himself.
So when it comes to being in a relationship with a narcissist, the same rules apply. Everything his spouse does and says is used to define oneself. Many victims notice that narcissists freak out for no apparent reason, assume insane things that he believes took place when they didn’t and etc etc etc. This is all due to then interpreting everything against themselves.
An example: you are going out with your sister for dinner. The narcissist will interpret this as you are lying and really out and about with another guy. This is because the narcissist has interpreted your actions as a reflection of who he is which is a lying cheater.
The common misunderstanding here is due to the narcissist interpreting your actions based on his real nature and not his false self which is what ends up confusing you. The narcissist only shows the false self, projecting his real nature onto you via gaslighting which constantly protects the false self.