How do you get hooked to a book?

[Guinevere]

How do I get hooked on a book?
I think that is best described by Tolkien himself in his wonderful essay "On Fairy-stories"

What really happens is that the story-maker proves a successful "subcreator". He makes a Secondary World which your mind can enter. Inside it, what he relates is "true": it accords with the laws of that world. You therefore believe it, while you are, as it were, inside. The moment disbelief arises, the spell is broken; the magic, or rather art, has failed. You are then out in the Primary World again, looking at the little abortive Secondary World from outside.

And the LotR itself is the best example of a fantasybook that has the inner consistency of reality.