Many years ago, I was fortunate enough to find the Shambala version of Basho's Oku no Hosomichi (Narrow Road to the Interior) translated by Sam Hamil. Probably the most luminous piece of writing I've ever read, each word a perfect translation of meaning, not definition. I'm still looking for the guy who'll do that for Aristotle's Poetics. Create a translation that makes sense or at least isn't some weird hodge-podge that sounds like Yoda speaking in tongues. Then I rediscovered unity of action. Because of the work I'd been doing in core events and probability—it jumped out at me. Talk about obvious.
Unity of plot does not consist in having one man as its subject. An infinity of things befall that one man, some of which is impossible to reduce to unity; and in like manner there are many actions of one man which cannot be made to form one action. One sees, therefore, the mistake of all the poets who have written…similar poems; they suppose that, because Heracles was one man, the story also of Heracles must be one story.
Because Kim is a person, events swirl around her like a hurricane. She's a former wife, mother, neighbor, daughter, student and small business owner. She goes grocery shopping, paints her nails, gardens and sends cards to her nephew. But, despite the fact that she's living her life doesn't mean that everything "in" her life goes in the story. If she drops a cabbage at the store, it lands on her foot, rolls away and knocks down a pie display it's not part of the unity, because it's not part of the story I'm telling.
The story I'm telling is about Kim's growing relationship with Jason and his daughter, Tyra. I've layered the basic storyline with Kim's transformational arc and her emotional journey, but it has nothing to do with cabbages. However, Kim's knowledge of plumbing, tile-work and toilets has a lot to do with the story because Jason is a contractor and I'm defining the shape of the story with Kim's need to get the bathroom remodeled. She's seriously invested in getting the B&B open, but she doesn't know how to replace a toilet and has less interest in tile-work.
I could use the cabbage scene. It shows Kim's personality, reveals a lot about her food likes and dislikes and it creates pressure that reveals personality. But it stands outside the story. Kim might be buying cabbage to make a reciprocal dinner for Jason, but getting stressed out over destroying a pie display so I can show how Kim deals with being yelled at doesn't necessarily mean the Kim revealed by this particular conflict is the Kim in my story. Cabbages don't mean a lot to Kim, and she's been through a lot. Some random bakery manager yelling at her would probably trigger an apology and a large pie purchase.
Jason yelling at her because he loves her and she won't let go of her ghosts is different, because the conflict is pertinent to the story (she won't let herself love him) and so is the character she reveals. Unity of action is a narrowing process. All the conflict in Kim's life doesn't belong in her book because it doesn't form a unity of action (plot as a selection of story events) which shows us who Kim is for the story I'm telling. There's still a huge amount of probability in the story--because each time Kim reacts to something it creates a set of potential outcomes. Unity is simply the way to select what is, and isn't important.