new things."--Ally Carter.
One of the most important things a writer can do is to allow their characters to experience growth. If your characters aren't evolving, learning from their mistakes (or making them for that matter), and facing forks in the plotline along they way, then you may want to think about making a major overhaul to your manuscript. People want action, drama, and suspense. They want to build a personal relationship with your characters. That's why people read, to take them away from the usual. Reading is an escape, a retreat to the recesses of creativity. For the most part, we all lead ordinary lives. So, if you audience is reading a book riddled with characters displayig more of the same, what is the incentive for them to continue reading? Afterall, it wouldn't be offering them anything other than a time-killer and who wants their book to be considered nothing more than that?
In short, if your writing and characters aren't moving into exciting new territory, your readers will.