I'm sure that's true in some way for everyone in creative pursuits whether working with pen or pallet. I suppose above all it's a psychological process, not mystical or magical. Though I certainly wish I could perform some sort of creative alchemy to bring seeds to blossom more quickly and with more frequency.
For me, it's often the creative stimulation of other writers and creatives that usually provides the final impetus to take seed to story. In what are now the old days for me, I used to produce a story after each major convention, World Horror, World Fantasy etc. Some have seen light and others not, but they were always satisfying. "Skull Rainbow" became a collaboration with Wayne and ultimately earned us a Year's Best Horror honorable mention.
The creative magic proved true again when World Fantasy was in Austin a couple of years ago. An idea based on a news item I heard on TV while Christine and I were on our honeymoon in 1991 became a short tale.
While I was in school last week, we had an assignment to read a couple of authors including Borges and produce a piece of fiction that pushed to the outer edge.
I started one piece but threw it away because another idea crowded it out. That was a piece based on a news story I read while in San Francisco in 2006 or so. It was one of those true stories that had haunted me in much the way Harlan Ellison was always haunted by the tragedy of Kitty Genovese, who died of a stabbing while a host of people looked on without acting. Ellison penned "The Whimper of Whipped Dogs" about the Genovese incident.
My little piece, "The Desk," drew some positive responses when I read it in class even though I stumbled over some complex passages. After a little more polishing I'll get it in the mail, snail or electronic as required.
It was a completely satisfying process, more satisfying than the struggle with a novel can be.
How does it happen? It's certainly different for each writer because everyone has varying degrees of output.
If I could somehow bottle it all or refine the process, well, I'd need help marketing the elixir for starters, but it would save a little time in the gestation.
The takeaway: Keep your eyes open, I guess. You never know what will plant the seeds that the magic will find.