Sometimes it doesn't. Sometimes it's like pulling up a bucket of muck from the bottom of a pond, hand over hand on an old, bristly rope, all the way up to a third floor balcony with a waist-high-rail (no, don't ask why anyone would haul a bucket of muck up to a third floor balcony. It's a metaphor, not an anecdote. It's the feeling of heaviness, of mental muscle fatigue, of sweat in the eyes and running down the back and the fear that the rope will break before you get it done.)
Oddly, readers can't tell the difference in the final product. (They've said things like "Oh, I'll bet *that* one was fun to write" andjust smile and don't tell them that that one was a struggle from the first word to the last, because I've found that they want to believe it's all easy.)
But I can tell the difference. One kind of writing energizes me. The other kind exhausts me.
Into every writer's life, these two experiences come...and every gradation in between, if you write enough stuff, long enough. I started writing when I was first able to write--so we're talking something in the range of 57 years of trying to write stories and poems and plays. Much of that time, what I wrote wasn't any good, but it was fun to write it. (Another truth: just because it feels good while you write it doesn't mean it's good writing--and the reverse is also true. How you feel while you write it has--as near as I can tell--nothing to do with the quality of the product.)
I keep feeling (erroneously, obviously) that it shouldn't ever be that hard now. We're talking over 20 years of being a published writer...counting the nonfiction stuff, over 25. Surely be now, I know how to do it--I should be able to take the assignment ("write a short story x words on y topic" "write a novel of x words in y setting with z protagonist") , gather up the reins of the story team, and trot briskly down the correct road to my destination...shouldn't I? So many words a day, all of them reasonably close to what they should be, all of them on track...? Carpenters with twenty years' experience don't have patches where all their nails bend or they can't get the boards together correctly; cooks with twenty years' experience don't burn the potatoes or forget how to saute onions; plumbers don't have days when they create leaks instead of fixing them. (or do they?) Surely a writer of experience should be able to just, you know, write, without the angsty bits.
Mind you, this is not an admission that's going to sit well with people who are aching to be published, and really do not want to hear that being published doesn't solve any inherent problems in their writing (or the rest of their lives.) "How dare you whine about that when some of us would give our right arms to be published?" I've heard when other writers and I have talked about the typical problems of a working writer. And I can sympathize...every published writer was an unpublished writer once, and we do not forget how we felt (one thing writers are very good at is remembering how they felt...)
But the truth is that writing will sometimes be difficult for even the best writers, and finding the writing difficult is difficult in yet another way--it brings doubt of one's own ability. Until a work is published (or at least until an editor has said nice things about it) nobody but the writer knows how the work is going. When a story acts like a reluctant overloaded donkey, planting all four hooves in the ground and refusing to budge, the writer has to fight panic as well as the story itself. What if--the primal fear at the root of all writer-fear--what if the talent has gone? Forever? What if writing will never be fun again because you've lost it?
No matter how much I've written, ever since my early, juvenile self-confidence was battered down, I've had the worry off and on that I could lose whatever it is that lets me write stories. It could just go away, water down the drain. It could turn out to have a "use by" date, and the date could be past without my ever knowing what the date was. Every time a story locks up, jams, refuses to go on and makes me drag it out, word by word, I worry that this is the one that will prove it's all over.
Maybe it's supposed to be this hard. Maybe, if the readers can't tell which bits were hardest, it doesn't matter.