One of things I’ve found interesting about reading fanfiction is seeing different people’s takes on a character. This can even become apparent in seeing fan reactions to new stories/episodes/sequels/etc—some like it, some complain that a character has changed (the more adamant even claiming the writer(s)—in many cases the one(s) who invented the character in the first place—has gotten the character wrong).
You see, for any (significant) character, the writer has probably delved into vast screeds of back-story and analysis that colours how they expect the character to behave. The audience usually doesn’t have access to this information (which is fortunate, as it probably doesn’t make for exciting reading), so will fill in gaps with their own preconceptions, expectations, and assumptions.
We do the same thing with real people. Note that I’m not saying this is wrong; we’d find it much harder to empathise if we didn’t (as we’d have no frame of reference). It’s essentially the “putting yourself in their shoes” idea; the more you know about them, the more accurate the metaphorical shoes will be. It’s another of the sensible cognitive shortcuts that help us deal with the world around us. The only problems arise when the other person’s experience is so different to ours that we make completely wrong assumptions about them, and the only way to correct this is to be aware of the error, and be open to learning something new.
Which can be hard to do, especially if you’re a white male in western society (which keeps telling you you’re the norm), but it’s definitely worth it for the chance to see the world from a new perspective.