I knew if I wrote it all down exactly as I dreamed it, it would be a pretty decent novel.
I woke up, and knew if I inverted half the dream--following a different character than the main princess as my protagonist, basically--it would be a GREAT novel.
And what happened? After telling myself I'd remember, I forgot everything. Absolutely everything.
Everything except the image of the girl crashing with a wave over the bow of a ship, and watching the seafoam slip away around her bare feet, and me, in whatever character I was inhabiting, thinking, "She's arrived!"