This started life as a comment on one of those 'you should be grateful you got anything, a story belongs to the original writer and them alone' type posts, but it turns out I have things to say about ownership of stories, so here's this:
Nah, I call bullshit. When you write a story and then put it out there, it becomes other people's as well; everyone who reads/sees it has a slightly different interpretation, sees the characters differently, feels differently about it. Once you let a story OUT OF YOUR OWN HEAD and INTO EVERYONE ELSE'S, it belongs to them, too. It LIVES in their heads; that's where it exists now. They can think what they want, say what they want, even write what they want-- new and different versions or continuances of the original story. And if you write something and it gets really popular... if it gets a whole fandom built around it by those people, who write more in that storyverse and make art about it and create headcanons and yell about it to each other, then that story belongs to those people, all of them, more than it ever did you, who just wrote a thing that started it all. It's like a child; you might have given birth to the thing, but now it's alive and out in the world and you simply don't have the right or ability to control what it does, where it goes, or who and what it becomes. And sometimes there are people who love and respect the story far, far more than the original creator ever did, and the story belongs to them more than ANYBODY.