Until I encountered Chris Hazelton's webcomic, Misfile, I had literally not written any fiction since high school. As a science major and later a professional computer programmer, I accepted that I simply didn't write fiction. It didn't interest me, and as far as I was concerned, I had no ability. Then I started reading Misfile, and alternative story lines started coming into my head. I saw two in particular, but tried to ignore them, since "I don't write fiction." I even tried arguing with the characters, who seemed to be insisting that I write those stories. I told them that they should bother Chris, who was their real author. But they wouldn't let me sleep, so I typed out on of the stories, and went to bed, relieved. I was back at the keyboard an hour later, when I found that the second story was demanding to be written as well. I have now written six installments of my fanfic, and am working on more.
I am also working on an original story inspired by one of the ideas in Misfile, but otherwise totally unrelated. After some abortive attempts, I wrote a first draft as part of the National Novel Writing Month challenge to write 50,000 words in the month of November, and am now revising it and publishing it as an ongoing webnovel: Take a Lemon.