I was struck the other day by something I hadn't really thought much about. How, in real life, we only know pieces of someone's story, fragments. We see whatever they choose to present to the world, what they want the world to see. We don't know the inner workings of their minds, their motives, their quiet private moments.
But in fiction, we get to experience that, as readers. We're allowed to peek into a character's mind, know his thoughts, see his fears, dreams, weaknesses, motives.
And I think that's partly why fiction is such a popular medium. We, the readers, are able to experience something that we're not able to experience in real life. We "get to know" characters personally, intimately, sometimes moreso than people in real life. And something about that can be very satisfying.
Of course, for writers, that's the beauty of fiction--that we're allowed to create these characters from scratch, get to know them, then reveal whatever we want about them to the reader, and let the reader get to know them intimately, too.