During my college course wanderings (the American tradition of “What the hell do I want to do with my degree?”), I took a few of economics courses, most specifically macroeconomics and socioeconomics. In other words, “Big Picture” economics. To be honest, I don’t remember as much as I should, but the one concept that’s always stayed with me is opportunity cost.
Now, what the heck does this have to do with writing?
I’m glad you asked.
Opportunity Cost is what you give up to do something else. It’s the value of everything else you could be doing instead of what you choose to do. For example, when I choose to write, I’m giving up the opportunity to take care of practical needs (laundry, grocery shopping, cleaning) or indulge in hobbies (reading, taking a walk, watching a movie). The opportunity cost of my writing is the time, energy, and money that I need to do it. Every second of every days comes with opportunity costs, and we’ve learned to make decisions almost instinctively.
“This is what I have to do now,” I think. “So this is why I do it.” But that’s not really the reason why. I do what I do because I’ve determined, based on everything else I could be doing, that this is the best choice at the time.
Each of the above examples (laundry, movie-watching, grocery shopping, etc.) comes with its own set of opportunity costs, and all the options must be weighed. When I think of all the daily intricacies involved, I’m amazed by just how much is processed and decided without our conscious awareness.
However, I didn’t bring up this topic to discuss my personal decision to write, but as a way to look at character development and to interpret GMC [Goal, Motivation, and Conflict]. The opportunity costs involved with the actions of a fictional character are exponentially greater than those of my own life because the possibilities are limitless given the very nature of fiction.
Our characters do what they do for a reason, and they’re often consciously unaware of active decision-making just like the rest of us. The decisions of which they ARE NOT aware are as important as the decisions of which they ARE aware. Their conscious decisions are external GMC; their unconcious decisions are internal GMC: their character traits and their personality as it’s been influenced by their personal history.
The reason why your character is unaware of certain decisions is because those decisions have become instinctive and habitual based on her past experiences. She’s learned to think or act a certain way without wondering about it, and it’s often when she realizes that she’s behaving or reacting abnormally, when she becomes conscious of her decisions and the opportunities costs involved, that the relationships within the story become important.
A character arc requires the eventual self-awareness of a character’s motivations before she’s able to change and grow, and it’s the realization of the opportunity costs of her decisions that sparks that awareness.
It’s the best thing to come out of economics class since supply and demand. 
