The Law of Unintended Consequences in Film: Three Examples and Three Exercises
“The Law of Unintended Consequences” sounds more complicated than it really is, but this principle is important to understand because it can be a goldmine for screenwriters.
In short, the law is this: an action will invariably have consequences; some of these are likely going to be things that were never considered before taking the action.
This is often referred to as second-order effects (and of course there exist third-order, and so forth) or knock-on effects. These are all essentially ways to describe the same thing.
Now when we turn to screenwriting, it’s worth acknowledging that the writer invariably spends a lot of time figuring out what specifically would play out given a character taking a certain action. The reason that the Law of Unintended Consequences is useful here is that it describes effects that–at least in retrospect–are undeniably related to that initial action.
They fit. They work. They don’t seem forced.
Sometimes this is through hubris. Sometimes it is a genuine lack of awareness. Sometimes it’s an impulsive decision that seems right in the moment. But then the chickens come home to roost.
Getting the right thing to happen at the right time is hard. But sometimes the unintended consequences are, to mix metaphors, precisely the chickens you need to get your leg over the fence.
One thing you’ll notice is that many films have the unintended consequence at the midpoint–this is often the perfect spot for an unexpected, gut-wrenching effect. However, this is not necessarily always the case, as we’ll soon examine.
With that in mind, let’s look at three examples. Nothing newer than ten years old, so rest assured: there will be spoilers.
Jurassic Park
The big daddy of unintended consequences.
Yeah, there are dinosaurs. We got that much from the poster. The problem isn’t the dinosaurs, it’s the way they were recreated: the DNA strands were incomplete, and the scientists rebuild these with that of frogs.
Add in the fact that the park is protected insofar as the dinosaurs are all female to prevent mating.
However, what the scientists failed to realize was–oops–some species of frogs, when in single-sex environments, spontaneously switch biological sex.
There’s a midpoint twist for you: in an environment of all female dinosaurs, a male dinosaur can appear–and now there are babies.
Back to the Future II
When Marty buys a sports almanac in 2015 so that he can win a bit of money off some harmless bets. What he’s not counting on is that elderly Biff steals the guide (and the time machine) and gives the almanac to (Biff’s) younger self.
The younger Biff knows what’s good for him and uses the almanac to become wealthy and powerful, turning 1985 Hill Valley into the sort of dystopia you wouldn’t actually see in America until the 2020s.
Notably the first act of the film is in 2015 and this marks the Act II break. Note how the meat of basically the entire film can be based on unintended consequences.
Ex Machina
Nathan creates Ava, an artificially intelligent robot. He brings Caleb, a gifted coder, in to test Ava. However, as Caleb learns over the course of the film, the test might be different than he thought–and more than he bargained for.
Interestingly, however, once we understand the true nature of the test it’s already the third act of the film. The unintended consequences are multi-fold, as Nathan receives a suitable answer to his question but at the expense of his own life while Caleb’s own cleverness puts him in a tight spot (so to speak).
Exercise 1: The Everett Interpretation of Quantum Mechanics
Not to scare the living shit out of you with physics, but Many Worlds matters. Hugh Everett’s 1957 Princeton doctoral dissertation proposed that, in short, every possible outcome from every decision or action actually literally (not figuratively) happens.
The result is that there is an inaccessible space somewhere–call it a “dimension” if you like–where every possible occurrence on every possible timeline has happened.
(Obviously we seem to be on the worst-case scenario one, but that’s neither here nor there.)
Presumably if you’ve seen enough spandex films, this type of thinking is second nature.
You can also watch Alex Garland’s DEVS or ST:TNG’s S7E11 “Parallels” for a good primer on the implications here.
Exercise: consider the timeline of your story. What is one tiny change–in your script or before it starts–that could have made everything else different? Which is the story of the true unintended consequence?
Exercise 2: The Butterfly Swarm
Consider the Butterfly Effect—the idea that a butterfly flapping its wings in Brazil can cause a tornado in Texas.
But don’t forget scale. A single, seemingly irrelevant decision can–and often does–set off an avalanche. Notably, sometimes it isn’t even the protagonist who makes the choice. Cf. Biff in BTTFII.
Exercise: Choose a small, seemingly trivial decision made in your story—by any character. What unexpected outcome could result four or five scenes later? What might this trigger that becomes the protagonist’s problem, even though she wasn’t responsible for it in the first place?
Consider how this feeds into Act II rising/falling action or even the Act III climax.
If you’re feeling special, find a situation where the original action is completely forgotten by the time the fallout arrives. This plant/payoff will make the audience feel smart. Audiences like feeling smart.
Exercise 3: The Hero as Villain
Let the protagonist create the antagonist. Through–naturally–unintended consequences.
This is especially useful in morally ambiguous, character-driven stories. It forces the protagonist to confront their past actions and is ripe with thematic resonance.
Exercise: What decision could your hero make early in the story that unintentionally advantages/creates the villain? How does this affect the protagonist’s life? Does the villain blame the protagonist–like Harry in Spider-Man 3 blaming Peter for his father’s death–and is this accurate?
Unintended Consequences as a Thematic Tool
The Law of Unintended Consequences acts as a potent thematic engine.
Consider the following angles:
Ideals vs. Reality
Characters often pursue something noble or rational—but the outcome undermines their goal.
The Dark Knight is a masterful example: Batman’s surveillance plan works—but also costs him Rachel, causes Harvey’s downfall, and creates public mistrust.
Moral Hazards
The Law of Unintended Consequences is your best friend when exploring moral ambiguity.
Breaking Bad is an extended exercise in unintended consequences, with Walt invariably digging himself deeper as his shortsighted actions trigger situations that put him, Jesse, and his family at risk.
Plot Elegance
Audiences may not see the setup until it hits—but when it does, they feel the cohesion.
Parasite relies heavily on layered cause-and-effect: each family’s actions spiral toward a finale, yet nothing seems out of place. The consequences may be unintended, but they follow cleanly from the actions.
The Circle Closes
Consider the beginning of your story. See how you can close with a mirror of this:
Exercise:
Look at the inciting incident of your screenplay. Is there a way to echo that moment near the end, but as a consequence of the rest of the plot? For example, does this leave the character in a situation that echoes how she once treated another?
For a tragedy, does this mean that she experiences the very thing that she tried to prevent?