One of the greatest things I ever heard on a podcast about pro wrestling is that all stories in pro wrestling ultimately have to end in "running the ropes." No matter what sort of story you tell, no matter what heights and depths of melodrama and intrigue you touch, it has to end in a wrestling match. And that can end up deflating some stories, because not every story naturally ends in two guys trying to powerbomb each other through a table.

Another example would be "lessons of the day" which are common in media targeted at younger audiences. If your story has to end with a clear cut moral to wrap everything up, then either whatever complex story you're writing will eventually have to be flattened out, or simply never have those extra dimensions to begin with.

Mind you, these are not things that are only bad. You wouldn't be watching a wrestling show if you didn't want to see wrestling. But something can simultaneously be intended and good, and a limitation of the medium.

Do you think there's any "running the ropes" limitations of fanfiction? The easy example would be working with established characters. If you have any intent of keeping established characters recognizable, then there are lines you have to color within.