JOYCE CAROL OATES: The ideas that we get for short stories tend to be very short and abbreviated, and usually focus on a single dramatic incident. The ideas that we may get for a novel or longer work of fiction obviously have to have a different structure.
So you have the series, or even a sequence, of dramatic events that culminate in something near the end of that work of fiction. So basically, an idea might come very swiftly for a short story, but you would need a number of ideas, a number of thoughts, and a layering of impressions to construct a longer work.