Flat characters can kill your story before it even gets started, and they’re guaranteed to make an agent or editor stop reading your manuscript long before the end. It can be difficult to allow your characters to develop naturally when you have a wonderful idea that you want to move them through, but it’s important to remember that as exciting as your story may be, there needs to be a reason for your characters to do what they do. You can’t have them act only to serve the story in your head; those actions must make sense both in the context of the story and for the character you have written. And the best way to know what your characters will do in a given situation is to ask them why. Asking “why?” will tell you who they are.
Behind every action lies a motivation, no matter how small. Why do we get out of bed? Because we can’t sleep. Because we have to go to work. Because we’re no longer tired. Because we heard a noise. But when it comes to character building, you want to ask why a character is the way they are. What led them to the start of your story? Why have they reached this juncture? Why have you given them certain personality traits and skills? Why do they work in whatever job you’ve assigned them? It’s not good enough to say “because I said so,” because if that is the only reason for their actions, they are in danger of becoming cookie-cutter characters, cliches you move through the story instead of realistic characters who drive the story.
You create layered, nuanced characters by drilling down and getting to the core of who they are and what they want. Their goals play into the action of the story, but it’s even more important to know why they want those things, because that motivation is what keeps them from giving up in the middle of a quest or throwing in the towel when a relationship requires some work. Likewise, asking why will explain a character’s inability to sustain a romance or tendency to pick a fight when certain subjects arise. If you have a character who is vulnerable in certain situations, you want to know why. What in their past formed that part of their personality? A character with a particular skill set learned those skills somewhere; why are they so good at whatever it is?
Not all of these details will loom large in your story, of course. Some may appear as a detail in a conversation, while others might end up “extras” for your website, but you will know, and that knowledge will inform everything your characters do and say over the course of the work.
You won’t have all the answers before you start to write, either. Some will come to you as the story develops and your characters land in situations that require them to react. Those decisions might be obvious to you, or they might require some thought, but try to understand why they make the choices they do.
Other answers will only work themselves out while you rewrite and revise, in context to the larger picture of the entire story. Look for inconsistencies in your characters’ behavior. Does something happen to change their outlook or their approach? Have they tripped over some trigger that brings their past to the foreground? Or have you pushed them to some point merely to move the story forward? Later drafts allow you to check for consistencies of behavior and motivation, and to make sure your characters are changing over the course of the story in an organic way that fits both their personalities and their experiences.
As with real people, you will never know your characters completely, but if you ask why they are the way they are in respect to the story you’re telling — why and how their pasts affect the present action — you will go a long way toward fleshing them out into living breathing beings who will engage your readers and draw them into the world of your work.