Have you ever planned to write a scenario, or an idea - nothing immensely specific but you knew vaguely what you wanted to do - and someone got there first?

Mm. No, never, but I have vague and constant paranoia about it. And of course you're going to feel miffed - that's a story that you already owned, in your mind, that you'll never get to write. That's tragic.

(Hm. Actually, JKR did use a minor plot device in Deathly Hallows I'd used in my WIP, which put me out slightly :-) Although I kept it anyway, and just looked unoriginal.)