Sometimes things go off the rails when the characters get bored. You’re in the process of getting them from plot point A to plot point B, and while you’re transitioning, they decide to go off in a different direction.
Sometimes this happens because the way you’re getting between the major plot items isn’t their thing. Sometimes it’s because they loathe the next plot point and will do anything to avoid it. Whatever the cause, you will often find yourself with characters who have turned the car into the parking lot of the nearest Denny’s and are about to rain down their own variety of madness on the poor, overworked locals.
It tends to happen to me when the main characters’ personalities don’t quite mesh up with the story plot. The question then becomes, do I change the characters, or the plot? Is there anything I can do to save it all?
This is probably part of why I end up not finishing so many stories. I will have to think on this.