I think we ought to only read the kind of books which wound and stab us. If the book we are reading doesn't wake us up with a blow on the head, what are we reading it for? So that it will make us happy, as you write? Good Lord, we would be happy precisely if we had no books, and the kind of books that make us happy are the kind we could write ourselves if we had to. But we
need books that affect us like a disaster, that grieve us deeply, like the death of someone we loved more than ourselves, like being banished into forests far from everyone, like a suicide. A book must be the axe for the frozen sea inside us. This is my belief.
Kafka, 'Letter to Pollack'.
Thanks to the H-Net listing for alerting me to this quote.