A well-known quote from Franz Kafka:

"A book must be an ax for the frozen sea within us."

Great quote, often quoted out of context. Here is the complete quote:

"I think we ought to read only the kind of books that wound or stab us. If the book we're reading doesn't wake us up with a blow to the head, what are we reading 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 within us. That is my belief."
Letter to Oskar Pollak (27 January 1904)

I go back and forth on Kafka's mindset. Was he really the despondent and man of low self-esteem as he portrayed himself in his diaries and to lettters? Or was he, in fact, quite self-assured?

Consider this:

"I am so miserable, there are so many questions, I can see no way out and am so wretched and feeble that I could lie forever on the sofa and keep opening and closing my eyes without knowing the difference."

But also this:

"The special nature of my inspiration is that I can do anything, but not toward a particular piece of work. When I randomly write a single sentence, for instance, 'he looked out the window,' it is already perfect."

I just finished reading Reiner Stach's magnificient three volume work (nearly two thousand pages) on the life of Franz Kafka, and I still don't know the answer to that question. But I think Kafka was both, i.e. he knew he was a literary genius, but he was also filled with self-doubt, unsure of whether he could consistently plumb the depths of his creativity, depths which he knew were literally boundless.