Often screenwriting isn’t a neat linear process. You don’t necessarily sit down and think up A followed by B and therefore C, etc. Perhaps you wake up one morning and you know what C is, but you still haven’t a clue why.
Sometimes the best way to write a beat or a scene, is to start at the end and work backwards in small steps from there. Reverse engineering, as it were. For example, as I’ve found in recent weeks, if you’re working towards a cliffhanger, it can help to know in advance what the cliffhanger is going to be.
For whatever reasons, it makes a difference when your focus changes from, “What happens next?” to “What happened before?” It’s perhaps a more logical, conscious approach, because you’re looking at the result of an action and trying to decipher what the cause could have been. Like a detective reconstructing possible scenarios from clues at a crime scene.
The principle is the same whether you’re writing for animation or live action. You have a specific image or turning point which you feel just has to be in the script. Perhaps the genre demands a particular set piece. A car chase, a first kiss, a murder. Maybe you have an important reveal that needs to be cleverly hidden. A hidden identity, a family secret, a betrayal.
At a less detailed level, perhaps when you’re outlining, reverse engineering is sometimes also the best way to plan out a sequence or even an entire screenplay. Maybe you just have a few big scenes in your mind, tent poles on which you want to hang the rest of the story. In that case too, looking back at how the action in the scene came about, can be enlightening.
Whatever the reason that you know your narrative destination, what happens when you work backwards is that your options are pleasantly narrowed. I say pleasantly, because sometimes an endless number of options can be daunting. Knowing the result before the action that led to it, focuses your creative faculties on possible causes, which by definition is a more limited set of choices than possible outcomes. Especially given the nature of your story world, the point in the character’s development, and other limiting aspects of your story.
On the other hand, the danger of this approach comes from precisely the same place as the benefit: its rationality. If the outcome is predetermined, and therefore your options limited, there’s a risk that you might not come up with the kind of unexpected twists that you otherwise would. But hey, sometimes an element of predictability is precisely what you want in order to be able to play with the audience’s expectations.
Of course, this being a screenwriting technique, it’s not a rule and it’s not always the appropriate method to choose. It’s just one of many ways to approach the task at hand. The bottom line, as always, is: whatever works for you.