I think the mind works this way about every thing. Like we don't relate to a friend based on what they do every minute of their lives. We relate to them based on the construct we have of them that gets comprised of memories and emotions and interactions with them over time. Which is often good enough.
BUt sometimes we get into a bit of a rut and start relating to a friend based on who they *were* years ago, not who they *are* today.
This seems most pronounced in family relationships. Stop some random person off the street, ask them to describe their mother or father, then go meet their mother or father, spend some time with them, get to know them, and you will invariably have a moment where you're thinking "what was that person off the street *talking* about? Their dad isn't anything like that." Or similar.
That we relate to everyone through the construct we created in our own mind is probably why you see some relationships go a lot longer than you would think. Know a married woman whose husband is a complete jerk? But she stays married to him? She might be relating to her image of her husband in her mind (he was so sweet on our first date), rather than relating to how he actually treats her now.
Part of that I think comes about because our mental constructs are not video archives of everything we ever interacted with that person about. There's a lot of data compression going on. A lot of data that is ignored. The thing about how important "first impressions" are? First impressions populate our initial constructs of other people, and we have a tendancy to ignore a lot of information that comes in after that. Our construct of a person might not match their behavior, but we'll stick with the construct rather than update it with new information.
With someone famous, I think we use that same mental ability to create constructs of everyone we relate to, but we populate it with information that we think we see in them during an interview or fourth-person-removed gossip that someone else said about the person. This is where the mental construct can vary wildly from the actual person, because its populated with third hand information.
The thing is, everyone you know, from your parents to your siblings and family to your best friends to your soul mate to some fan who never met you, they all relate to you through their mental construct of you in your mind. The difference is that we don't usually see the full details of anyone else's construct of us. With a celebrity, fans tend to express their opinions about the celebrity, and in doing so usually reveal what their construct of the celebrity looks like.
Most people don't sit down and say "tell me about your mother" and then go interview your mom, and then determine how far off your construct of your mom is from who your mom really is. When a fan writes about their favorite celebrity or when a anti-fan writes about someone famous they hate, they're revealing what their construct looks like, and if you happen to be the object of that affection/disaffection, then you get to see their construct and how far from reality it is from who you are as a person.
Assuming all this is true, I don't know that knowing any of it actually give us enough information to change it. But it might at least help grant some understanding about it.