This is kind of like the question about the chicken crossing the road. A hundred different people would give a hundred different answers and then the 101th person would turn up and ask, "So why did the chicken cross the road?"
I just finished reading the Kite Runner. At the beginning I was detached. Who would like a MC who can't stand up for himself? Who is envious of a loyal friend? By the last page I was marvelling at myself for actually rooting for Amir-the protagonist. He was flawed. He made all the wrong choices. He was a coward. BUT. He was frustratingly real. And that is what I think made the book rock. If I would have attempted a similar story, I'm pretty sure I would have messed up withing the first two lines itself. (Side note: The opening lines are surreal!)
The thing about great books is that they don't throw you in a different dimension, completely ripping the fabric of your own existence; they lull you into an alternate reality. The best ones make you forget about time and space. One minute you flick to chapter one, the next you're gazing at the last page contemplating how hours flew by unnoticed. And then there is disorientation. You walk out of the room/library/coffee shop and realise that life is going on as usual; that people are scampering here and there completely oblivious to the gem in your bag. It's a strange feeling, that numbness... As if you have just bid adieu to a best friend. You stare at the cover for minutes and then shake your head in disbelief, or maybe smile to yourself. And then days or even weeks after this escapade you pick up the book from your shelf and lose yourself all over again.
Those are the books I love to read.
Those are the books I dream to write someday.