Writers don’t talk about this question too much. Much more fun and entertaining, after all, to complain about the difficulties and pains; who doesn’t like people to feel sorry for them? But the quote below (with my emphasis added) excerpts an answer from Jon Fosse, at the Poetry International Web (sorta awkwardly translated by May-Brit Akerholt, in my opinion, in comma-spliced and run-on form):

…when I write something I feel is well written, something new has come into the world, something that wasn’t there before, I have, as it were created existence, and this, the joy of writing people and stories, yes, whole universes no one knew about, not even I, before I had written them, surprises me, and gives me joy. No one knew about this, not before I wrote it. And where does it come from? I’ve no idea, because it is new to me as well. I probably hadn’t thought about it before. Writing, good writing, will therefore always be a place where something unknown, something which didn’t exist before, is given existence. And that, writing as a state where something, yes in a sense even a whole new universe, is created and given a kind of existence for the first time, is perhaps what I enjoy most about writing. A whole new universe comes into being every time you write well. Because all good texts, yes poems too, are in a certain sense a new universe, which did not exist before, but which is created in good writing.

I’ll add: for me, one of the great joys of reading good writing lies in experiencing, vicariously, the writer’s delight at the moment something unexpected happened on the page or screen. I think I sense this sort of exclamation-point moment in books and other “formal” writing, but I’ve also seen it between the lines in casual text: text messages and chat sessions, one-off blog posts, and yes, even some Facebook status updates and Twitter posts.*

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* Sorry, Froog. :)