Doctor Who Fandom Curse: Knowing that at some point your Doctor will have to regenerate.

Supernatural Fandom Curse: Knowing that someday your series will end. And soon.

Avenger Fandom Curse: Knowing that Joss Whedon will likely kill a favorite character.

Twilight Fandom Curse: Knowing that you will never win a fight against another fandom, ever...

Harry Potter Fandom Curse: Knowing that it will never be as good as the first time around.

Sherlock Fandom Curse: Knowing that after waiting for ever you will only get about three more episodes with another cliff hanger even worse than the previous one.

Glee Fandom Curse: The show.

LOTR Fandom Curse: Lying abandoned and forgotten in a dark pit of Tumblr while waiting ten years for the Hobbit.

Hunger Games Fandom Curse: Knowing that your favorite character will either die, go insane, or never be seen again.

Game of Thrones Fandom Curse: Knowing that everyone will die. That's it. Everyone dies.

Homestuck Fandom Curse: Does this really need to be explained?