Generally, I come up with a great idea, at least I think it is, but then BAM I see this same idea the next day or something on a show or in another book. Most recently I had the idea to use incarnations of the seven deadly sins in an upcoming story (don't ask which one, Rune, else beware spoilers
), but then I realized each of the sins were portrayed in FMA. Granted, the homunculi are merely named after the sins. But if I decided to go through with this idea, to me it feels like I'd be copying too close to FMA. I've come up with a decent substitute (again, don't ask 
).
But this was not the first time. Because of Tolkien I can't put elves in trees, so I'm putting them in deserts (Elfquest doesn't count as doing it first
).
I came up with a reptilean alien race for some sci-fi stories, and then Farscape came out with the Skarens. I've altered my race enough, but it is still a hassle.
So what is the moral of the story?
If you look hard enough, every idea has probably already been thought of. The best you can do when you discover this is make slight alterations to your own idea to make it a similar yet distinct version. You cannot get discouraged in the face of a situation like this. Either make the idea your own in a special way, or present it in a fashion that is an obvious homage to a predecessor.
