I thought of another example of how the Writing Fairy pays a surprise visit to your story and throws a monkey wrench into the flow - which turns out to be a good thing.
In Me and Rupert Goody, I was writing along and all of a sudden a sentence popped into the story about Rupert repairing a hotplate for Uncle Beau.
I hadn't planned that.
I hadn't thought about that.
I had absolutely no idea where that hotplate came from or, more important, why the heck it was there.
......the climax of the story turns out to come when Uncle Beau's store burns down.
Why did Uncle Beau's store burn down, you ask?
BECAUSE OF THE HOTPLATE!
Dang, that Fairy is pretty smart.
(P.S. I fixed that link to Sara Lewis Holmes's blog entry that was referenced here, in case you missed it.)