First Impressions, Ongoing Impressions

Another mind-bender that humans too often do to other humans, but Narcissists do to an intense degree:

Treating others (especially targets) as if they are NOT the person that they really are.

Human beings "mirror" one another and give feedback to one another every time we interact. I smile, you smile back, it's normal, it's polite, and you are signaling that you SEE me and acknowledge me and my expression. You are giving me normal, straightforward feedback and reciprocation, no drama there. If you see me doing a task, you would acknowledge that I'm doing that task, and you would store it as a simple memory about me~ "She washes dishes, she knows how to wash dishes, she washed them today". You would gather bits of information about me that way, and put them under a category in your memory of "who she is, what she does". (You wouldn't assume much about my character or my preferences, or my strengths or weaknesses, you don't have any of that information. You wouldn't assume that I CAN'T do something, it wouldn't cross your mind, you have not seen me try hard and fail at something.)

This is how we build our "pictures" of other people, when we are doing it in a healthy way.  We don't make a lot of assumptions about them for good or for ill, for strength or weakness, we simply slowly take in bits of information as they come, and store them in a neutral, drama-free memory file.

"He likes dogs, he has a Bichon Frise."
"She plays guitar and piano, she has been playing since she was very young."
"He cooks, he likes to cook. I enjoyed the gourmet meal he made."
"She worked at the bank as a Loan Officer."
"He always calls and shows up when he says he will, therefore I feel pretty comfortable trusting his reliability."
"She remodeled my friend's kitchen and built another friend's deck, therefore I know she is skilled in remodeling and carpentry."
"He speaks politely and considerately when he interacts with me and also with others. I have not seen him act rudely or arrogantly."
"She has behaved  like a friend to me on several occasions, she has stood up for me, she treats others with consideration and care."

We build Pictures of others based on actual information when we are doing it in a healthy way. We don't assume a person CAN'T do something just because we've never actually seen them do it, or based on their appearance, nor do we assume they CAN do something based on our own fantasies because of the their appearance.

Controllers, Narcissists, and the immature (due to age or other) make their Picture of another person BEFORE they find out real bits of information. It's not based on anything but their imagination. You might remind them of a girl they used to know, so they put their "Picture" of who she was on YOU. Maybe you are wearing certain clothes, or a uniform, so they put the Picture they keep in their imaginations of "people who wear these clothes" on you. They might base their Picture of who you are on a combination of things, like your clothing, job position, weight, and gender, or just one or two things, like your hair color and your facial features.
This is what they go by when they interact with you. They don't go by what you actually DO, or who you actually ARE. They made their Picture up of you based on their own imaginations, they didn't wait to find out anything real about you at all. Sometimes they will also pick up rumors, gossip, or adulation from others about you and insert those into their Picture of you as well.

What do they do when they find out their Picture of you doesn't match who and what you really are?
Not much. They just ignore, dismiss, and delete the new information. It doesn't fit with their Picture they have in their head of you, so they reject it.  The most important thing to them is their comfort, and the Picture of you they created fit in with their comfort level and ego. The Picture is static, and it's for them, not for you. It's not about you, it's about them. Changing that picture would take serious effort on their part, and even more importantly, it would mean they were NOT CORRECT when they made up their Picture. CAN'T HAVE THAT, it's too uncomfortable. So, they will just REJECT any new information that would change the comfortable Picture.

With that rejection of information, the target also usually gets rejected along with it.

In other words, when a Controller or Narcissist keeps receiving information that proves the Picture they have created of someone else to be false, they often decide they don't "LIKE" the person anymore. A person with Narcissism can even become angry or hateful toward a Target when they turn out to simply be different from the Picture they created of them.

The Picture they create in their heads may have the subject being wealthy or poor, smarter or less intelligent than themselves, stronger or weaker. They might have painted the person in their minds as being a parental figure or a little sister or brother. They may have painted them as being skilled or unskilled, experienced or inexperienced. Crazy or very stable. "Good" or "Bad". Virtuous or promiscuous. Honest or dishonest. Sober or not sober. Their Picture is painted from the imagination, not actual information, so it does not reflect reality, it's hit or miss; it's really a reflection of their own inner world, their ego, the way they want the world to be around them.

So when a Controller or Narcissist (or younger person) speaks and interacts with you as if you are a different person than you really are, it's because they really don't know who and what you really are. They create their Pictures of others first, without actual objective information, and that's what they go by. A fictional Picture.
When your actions don't fit their Picture, they often become uncomfortable, and then will often put the blame for their discomfort on you, because in their minds, you are causing it.
You're messing up their Picture, you're changing the script they wrote for you, you're not staying in the place they assigned  you.

 It's important to qualify, however~ a "Socio/psychopath Narcissist" will often learn as much as they can about another person, purposely, so they can use what they learn to manipulate their target. However, so many of them are so befuddled with arrogance that they think they know more than they do; they usually slip up pretty early on and reveal their true intentions.