Externality is a term in the economy that means "the cost or benefit that affects a party who did not choose to incur that cost or benefit" (Wikipedia). Basically, it means that in economic activities/transactions, there are most likely other people/party that are somehow affected by the activity. For example, when you use Uber to go somewhere, you and the Uber driver are the parties that choose to engage in an economic transaction; you get the benefit of being in the place you want and the Uber driver gets the benefit of receiving your money. According to externality, however, there is another party that is affected by the transaction, in this case: the environment. The transaction costs the environment an air pollution because of the car's fossil fuel usage.
In this post, I would like to apply this concept to a whole different field: storytelling.
As you might know, conflicts are essential to a story. And it's often unclear what constitutes a great conflict. What makes some conflicts special, while others not. When I learned about externality, I couldn't help but think about its potential in making a great conflict. In fact, I already found them in some of my favorite stories. While there's a lot of stories that involve an externality in their conflicts, there's only a few that deliberately exploits it. Here are some of them.
Captain America: Civil War (2016)
This film started with the Avengers fighting Crossbones. In the final moment of the fight, Crossbones attempted to explode a bomb attached to his body. Wanda tried to move Crossbones to a higher place with her power, but it's already too late and the bomb exploded near a building and killed a lot of civilians inside. The casualties of this conflict ultimately drove the proposition of the Sokovian Accords, which is essentially the main plot of the story.
In this conflict, the willing participants are the Avengers and Crossbones, while the civilians around them are not. They are the ones affected by the externality of the conflict, which is significant to the story. Not only the externality triggered the plot forward, but it also greatly impacted the characters involved. Just like you would feel guilty whenever you're causing a pollution to the environment, Wanda blamed herself because her decisions accidentally brought dooms upon innocent people. As an audience, it's hard for us to blame her in this situation, but I'm sure it definitely succeeds in painting a grimmer picture of her character moving forward.
Harry Potter and the Goblet of Fire (2005)
In the final challenge of the Triwizard Tournament, Harry and Cedric Diggory were transported to a graveyard where the soon-to-be-reborn Voldemort and Peter Pettigrew waited for them. Voldemort who didn't expect Harry's friend's presence, ordered Pettigrew to immediately kill Cedric. While you might say that Cedric is involved in this conflict because he is one of the tournament's contestants just like Harry, one could also argue that the real conflict here is only between Voldemort and Harry. Voldemort had no intentions against Cedric and simply killed him because he's only after Harry.
Cedric's death means a lot for Harry Potter's story. First off, this conflict brilliantly introduced Voldemort as a menacing villain for the rest of the series. Cedric was only an unfortunate casualty in his quest for revenge against Harry. Second, just like Civil War, it greatly affected the characters that are involved in the conflict, namely Harry. I don't know about this, but surely Harry ever blamed himself for what happened with Cedric. And lastly, it triggered future plotline, where Cedric's father blamed Harry for his son's death and Harry's son tried to undo Cedric's death.
It's always interesting to see the past mistakes of the characters come back to haunt them in the future. This particular thing has been a seemingly recurring theme that is brought by externality where the characters couldn't help but feel guilty about the ones badly affected by their businesses.