It’s fairly common knowledge that most of an iceberg – seven-eighths is the usual number – is underwater, out of sight to all but the denizens of the deep. What’s less common knowledge is that most of a piece of fiction is likewise out of sight to everyone but the author.
Case in point: a short story Jim Macdonald and I finished not too long ago. Before I could do my part of the work on it, I ended up researching everything from the San Francisco earthquake of 1906 to early-twentieth century spiritualists in Denver, Colorado and using the results to construct an entire past history for a particular character.
And then I didn’t put any of it into the actual story, because none of it was stuff that the readers needed to know. It was stuff I needed to know, which is a different thing.
This is also one of the ways that a short story can differ from a novel. If we’d been writing a novel using the same general theme and ideas, all of that character history might have become a major plot thread. This is because a novel can do more than one thing at a time (which is why writing a novel sometimes feels like trying to juggle jellyfish) but a short story only has the room and the time to do one thing, and whatever isn’t directly relevant to that one thing needs to be uprooted without mercy. If you can’t uproot it without destroying the entire structure in the process, you probably don’t have a short story at all.
(If it isn’t a short story, but you’re certain in your heart and in your bones that it isn’t a novel, then you’ve probably got a novella on your hands, and an entirely different set of writing problems. But that’s a post for another time.)