Consistency. It’s a hobgoblin that can get in the way of creating interesting characters. Fledgling writers are told that their characters actions must be consistent. You’re not supposed to throw a monkey wrench in the reader’s expectations by having a character doing something completely unexpected and out of the blue, something so not the character you’ve established. And why not, pray tell?
The most boring people, in real life, are the ones who never surprise us. We know what they’re going to do from day to day, even from hour to hour, some of them. We know what they like and dislike, believe and disbelieve, and we know exactly what they’re going to say when they open their mouths. They’re the ones we avoid like the plague unless we’re tied to them by inescapable bonds of blood.
If we cross to the other side of the street when we see one of those perfectly consistent people heading in our direction, why in the world would we want to read about them? We would much rather read about the quiet, friendly neighbor whose house is suddenly surrounded by police before they break the door down and lead him out in handcuffs. They found three corpses in the freezer in his basement? But he seemed like such a nice man!
We will eventually learn a lot about our former neighbor, about his background, maybe about crimes he committed before moving to our quiet neighborhood. We will learn that we were beguiled by a facade that covered a monster. We never saw it coming, but we eventually come to understand why it all happened. That’s real life, repeated on an almost daily basis, confounding our expectations, jolting us out of our assumptions about what people are really like.
How well do we know anyone in real life? Haven’t we all met people who surprise us by acting completely “out of character?” How many marriages and friendships break up because someone has done something unacceptable and completely out of character? You can know someone for half a lifetime and still be surprised when they do or say something you never could have seen coming.
In fiction, if one of my characters does something unexpected, that means there’s an element of their personality or background I haven’t made you aware of yet. It’s my job as a writer to make sure that element is there, and to explain it to you in a way that relieves you of the need for a consistency that exists only on the surface.
For the writer, it’s an opportunity to go deeper and find out whether it’s really an inconsistency or something hidden that we’re now aware of. The important thing is to explain it, not just let it happen and then drop it. This is one of the uses of backstory. Done right, it will change your view of the person and add to the dramatic punch of the story.