... sounds like an Ellen Datlow anthology, or maybe an Arkham collection, but it's not. It's something that happens in the night when you're three-quarters finished with the first book of a trilogy and your thoughts stumble across A Great Idea... a Great What-If about the work in progress. And that tips out a cascade of other ideas that you soon realize will tie the books of the trilogy into a deliriously cohesive whole, so much better than what you already had planned.
Dreadful because you can't refuse, even though you know this will mean a major rewrite, adding new characters and scenes and subplots, pushing passages you've already written into books two and three, or maybe into the trash folder. No, you can't refuse because now that you've seen this, what you had planned before looks like crap.
Just letting you know, because this means you won't be hearing much from me for the next couple of months.
FPW
FAQ
"It means 'Ask the next question.' Ask the next question, and the one that follows that, and the one that follows that. It's the symbol of everything humanity has ever created." Theodore Sturgeon.