Focus is necessary – for you and your short stories and novels.
One way to maintain the focus of a plotline is to keep your characters enclosed, either by physical constraints or with a time deadline. Determining how long it will take for the arc of action to peak then resolve is one of the first details you should decide on when outlining your story.
A plot that stretches over months or years is going to give readers a very different story than one that only lasts 24 hours. Generally, a timeline that drifts longer and longer is going to make it more difficult for a writer, particularly an inexperienced one, to hone in on the key elements of the story. As a result, the plot can run astray.
In contrast, when you predetermine that the action will be wrapped up within a short period of time, you heighten the urgency of the story and the sequence of events involved in resolving it.
Likewise, keeping your characters in closed quarters where they cannot roam far builds tension, which will keep a reader turning the page, wanting more. That doesn’t mean you keep your protagonist trapped in an elevator for more than a scene or limit your story to a jail cell, but such uncomfortable situations are good places to spend some time. In many of Elmore Leonard’s novels, the movements of characters are limited. They’re stuck on an island (“Cuba Libre”) or in prison (“Out of Sight”, among others) or in a job they can’t leave (“Tishomingo Blues”). The core behavior of his characters is revealed in these circumstances and that’s an important point.
While the most immediate goal for constraining your characters is to rifle the plot along, this story-building strategy also impacts character development. People reveal basic instincts while under stress and it’s those instincts that make them unique and interesting. It’s through these high-intensity scenes that the reader gets to figure out the motivations of your characters. More importantly, it’s another way for writers to get to know the people who inhabit our imaginations and that helps to fasten them to the page.