Books are all about questions. You start with a “what if” and continue with a “who, where, what, when, how,” but if you don’t tell “why,” none of it rings true.

I just started a new book, and I’m really happy with the plot. It’s romantic, suspenseful, and original. Now that I have a basic, bare-bones outline worked out, it’s time to apply the Toddler Test.

To give a plot the Toddler Test, you pretend you’re three again and ask “why?” about everything.

Why does she leave her husband? Okay, he’s a jerk–but why didn’t she figure that out sooner? Why did she marry him in the first place? Why doesn’t she stay for her kids? And then why does she go to Wyoming? Why does she drive instead of flying? Why does she choose that particular town? Why, why, why?

After a while, I’m tempted to give the standard parental answer: because I said so. But you can’t do that in a novel. Yes, you’re the author and you run the show. You created these characters. They’re extraordinary people, and so of course they do extraordinary things.

But why?

Your reader’s not going to be any more satisfied with that reason than your toddler, and while your kid has to put up with you, your reader can throw your book across the room and tell all her friends you’re a talentless hack.

Characters in genre fiction do daring, difficult, and downright dangerous things; otherwise, the book won’t hold the reader’s interest. But even the most intriguing actions don’t engage a reader’s interest unless they’re grounded in reality by motivation. Without his troubled childhood, Heathcliff is simply a bad-tempered oaf; without his missing leg, Ahab is just a random whale-hater.

And asking “why” doesn’t just make your story better; it helps enrich your character, giving him dimension through a backstory that helps the reader sympathize with him and understand his actions.

Those three-year-olds are onto something.