Character People

You know what's kinda hard to do? To write a character that's based on a real person. At least it's hard for me. Maybe not other people. I've tried it several times-incorporating people I know into something I'm writing. And I can never feel like I'm getting them right.
You know the funny thing, in fanfictions, I don't have any trouble writing about other characters. I wrote the whole of Twilight Princess from Midna's point of view, and I got over 200 comments (!!) telling me how good it was. And That's not the only one. Whenever I write something with a character from a book, game, or movie, I can feel connected enough to them that I feel confident about writing their actions and dialogue.
I wonder why that is. That I can use other characters, but not real people. Maybe because in some way, characters in general are more shallow than real people. Or perhaps it's because that when you read or play or watch something, the person who made that tries hard to reveal that person's personality to the reader/player/viewer. So the viewer gets a better sense of what that character is like. While real people don't reveal their true selves all at once. If you don't know someone really well, in can take a long time to figure out what they're really like. Now some people, I can completely predict what they're going to do because I know them so well. I'm of course very good at predicting what my parents are going to do. I'm pretty good at doing it with some of my friends too.
Yeah. I'm curious as to what other people think. If you write about a real person, do you feel like you can accurately portray them? (If anyone is reading this).