I've been thinking about a physical analogy for the writing process, and here's the sort of lame idea that came to me:
If you bundle the plotting, characterization, everything that goes into writing a novel, then the process looks like this:
You have an infinite (or nearly so) stretch of flat ground in every direction (imagine standing by yourself on the salt flats with no distinguishable features, nothing but blue sky and white sand to the horizon) and an infinite number of bowling balls, as well as a just-in-time manufacturing facility for any color or size bowling ball. You want solid gold with swirls of purple ice? Done.
Page one...You got your special bowling shoes on?
So, you're standing in the middle of nowhere, white sand in every direction, and there's one of those bowling ball delivery systems...just coming out of the ground with any number of bowling balls. You can talk to it, too, ask for a bowling ball to represent your main plot line, ten more for sub plot lines, scenes, pivotal points, any kind of action.
On this writing ground that goes on forever, directions correspond to plot lines, and the kinds of bowling balls--color, patterns, materials correspond to individual plot elements, individual characters, actions, scenes, even lines of tension.
In the course of writing your novel, you're going to be grabbing a bowling ball and rolling it in a specific direction. In the beginning of your novel that's all you'll be doing, grabbing the next ball that comes up, pick a direction, get your stance, take your steps and release. The ball is away. Go back for another.
Now, let's look at what your novel looks like halfway through.
Here's the way it works. You can send fifty bowling balls off in almost the same direction--close enough that when the time comes to start wrapping up plotlines, you don't need to travel too far. You're a mile out and you have plenty of room and time and stop one from rolling forever.
You can send fifty off in roughly the same direction, and then turn and send another ten in the opposite direction. You still won't have trouble wrapping up your story, because you'll have time to cover both directions.
Now, if you're planning something grand, a series with plots that extend well beyond the current book, there's no problem sending bowling balls of many colors off in twenty different directions. You'd have to be a genius--and very quick--to close all those down with probability and reader satisfaction in one book. But in all likelihood, you want them to just keep rolling. You'll pick them up in the next book, maybe even give them a kick to change direction, or a shove to increase speed.
Make sense to anyone? No, I didn't think so. Me neither.