What runs a good story off the rails?
Actually, I think there a variety of things that can do it.
There's a story that runs on another site that after 40 something chapters, the hero finally hooks up with his true love, goes to the prom and then JOINS THE FRIGGIN ARMY. Ok- so I hate the military. But it had nothing to do with the story or its quality- IT WAS ME.
In another story that LOTS of people fussed about a much loved couple showed signs of breaking up. AGAIN- it wasn't the quality of the story, it was the emotional investment of the reader. You come to love the characters and hope for the best for them and then a little thing like REALITY that comes along and takes a great big stinky dump on the fantasy.
In another story that broke my heart, after many chapters and much angst, the perfect couple broke up. I don't have to read fiction to get sad, hell I'll just think about my own love life.
Well- if you get my drift here SOMETIMES it's not the story than ran off the rails, the reader just didn't like what happened. This is NOT the authors fault and the reader has to realize that every story just ain't going to turn out all hunkie-dorie.
A lot of authors don't do themselves any favors by cranking out chapters when they are just plain lacking inspiration. Been there, done that, got the t-shirt. I felt like if I didn't get out a chapter a week, my readers would be off to the next truck-driver romance they could find. NOPE. Wasn't the case. They are much happier to wait a while for quality than have something that isn't ready or is just plain uninspired foisted off on them.