My Characters Do What I Tell Them

A lot of writers like to talk about how characters do things that surprise them, or develop in unexpected ways.

I'm of the school of thought that a story is a thing you build, not a thing you discover.  When you write, you should know where you start, where you are going, and, at least roughly, how you are going to get there.  This approach helps you keep the plot tight and it keeps the characters consistent and logical in their behavior.

"So, lately, I've been studying the teachings of the Buddha."  

Characters don't have autonomy, and I think it's a mistake to treat them like they do.  They need to act in realistic and believable ways, and their actions need to be logical and supported by understandable motivations.  But they act in service of your objective, not the other way around.

The ever-helpful James Wood tells us that Nabokov scoffed at the idea of character autonomy; he viewed his characters as chess pieces or serfs to be moved around by the author. This is fundamentally true, but it's also a simple description of a complex process; the great trick of fiction writing is making contrived things appear organic.  Characters do what they do because the author and the plot demand that they do so, but, to the reader, the characters must appear to act for their own reasons.

The characters' arcs should be carefully planned to develop with the narrative and its themes.  If the character isn't who you expected him to be when you hit an important plot point, then the actions you need him to make to move the story forward might not make sense.  And if you're not sure who your characters are when you start writing, it's very hard to outline a plot with that seems character-driven.

That's not to say you shouldn't pay attention to how the characters are working, or shouldn't change them over the course of the writing process. Your characters and plots and themes all develop as you revise your story, and you should constantly be asking yourself if characters' actions are consistent, logical and spring from believable motivation.