I give you my best failed idea (reposted from an earlier "failed ideas" thread)

I invented a character who suffered from a unique but crippling condition (the working name of which was Blacksight, but it was too similar to "greenseeing" from A Song of Ice And Fire, so I planned on changing it eventually). The idea was that he could see the future (unwillingly, kinda like That's So Raven), but each time, the disjoint-in-time between his mind and body would cause violent physical symptoms and, in the worst cases, as his condition worsened, he would start losing memories; a sort of tit-for-tat system based on his visions. As things continue getting worse, he would start losing memories of the visions he just had, so if somebody wasn't in the room to listen to him ramble while the episode was happening, his vision and a memory would both be lost. After each one, there would be this sort of question mark in the air of what is it that he forgot now; sometimes it's something minor like how to tie his shoes or peel a potato, other times he would forget who people in the group are, or his own name (the name he had in the story was not his given name, but he had already forgotten his given name by the time his character is introduced; he had also forgotten who his parents were and where he was from).

I had the system all worked out and I thought I would be able to bring up really cool moral questions with it. What if his friends try to force a vision on him to get them out of a tight spot? What if he fakes a vision in response to this so that he doesn't have to lose a memory? What if he wants someone to kill him because of how miserable Blacksight makes him?

I loved the idea...but ultimately I realized it had no place in the story I wanted to tell. It deserved its own story; a character like this can hardly be as secondary as I had made him.

Edit: The character's name was Cheswyck, and went by the nickname Wyck. I never decided on what his given name (the one he forgot) was supposed to be, and that never mattered because it was never going to come up in the story anyway.