The first time I did NaNoWriMo, I wrote a fantasy novel. The premise was a land where everyone, except the protagonist, has magical powers. Then I found out that’s the premise of a published Jim Butcher novel. (Possibly a series of novels, I’m not sure.)
In 2008, my NaNoWriMo novel had the protagonist returning to his childhood, with all his memories of “later” life intact. There’s a Canadian TV show, Being Erica, with a very similar idea.
The other night, I jotted down in my journal an idea for a new poetic form — I thought. The form, cleave poetry, already exists.
I guess the only thing left to do is write Don Quixote.