In myth, the third act would be when Jason comes home with the golden fleece. As Campbell writes in The Hero With a Thousand Faces “The first problem of the returning hero is to accept as real, after an experience of the soul-satisfying vision of fulfillment, the passing joys and sorrows, banalities and noisy obscenities of life.” (218) There is a reconciliation as the hero returns to the old world with the tools of the new.
Campbell had a nice map of this progress.
Campbell suggests that there is a pattern for the monomyth, summing it up in three parts, which are often adapted for the three-act structure in film. “The standard path of the mythological adventure of the hero is a magnification of the formula represented in the rites of passage: separation- initiation- return: which might be named the nuclear part of the monomyth. (30)” He interpreted mythology as a precursor to psychology. He summed it up. “Mythology is psychology misread as biography, history and cosmology.” (256) He described it as similar to dreams, in terms of what it reveals about humanity, but with the crucial difference that at some point, there was conscious control in coming up with the story.
You could see this basic narrative in many films. The first part of The Lion King follows Simba as he is raised by his father. The second part features him as an outcast from society. The third part is the exile’s return. Campbell noted that early biographies of Charlemagne, Pope Gregory the Great and Chandragupta reshaped the lives of real individuals to tell this type of story. “Each of these biographies exhibits the variously rationalized themes of the infant exile and return. This is a prominent feature in all legend, folk tale and myth.” (323)
He describes how the return fits in many three-act narratives. “The mythological hero, reappearing from the darkness that is the source of the shapes of the day, brings a knowledge of the tyrant’s doom. With a gesture as simple as the pressing of a button, he annihilates the impressive configuration.” (336) That is often the final act of a film.
There is variety in terms of how to tell this particular story. The Lion King formula is the most straightforward, but you can also begin the story with the return of the exile. An example would be Grosse Point Blank, about an assassin attending his high-school reunion. Inception has Leonardo Dicapro’s character undergo a dangerous mission in order to be allowed back to the United States, so the return home is part of the end of the film, and the reasons for the exile are revealed in the flashback. The Searchers had a similar conclusion.
More mundane stories are, to a degree, a recent development. There weren’t that many myths about ordinary people in earlier days. In a more secular world in which we understand that we are not going to be gobbled up by shapeshifting wolves when we leave our village, the same basic structure might be applied to a story that’s far more realistic than the typical myth. Most stories are essentially about someone leaving their comfort zone. While in myths, it was to go to a fantastic land populated by Gods and monsters, in the real world, it could apply to any new place, be it a school, or new workplace.
Even documentaries like Gasland can follow this format. I’m aware that there’s some controversy regarding the factual accuracy, but that’s largely irrelevant when considering the story structure. In the film, Director Josh Fox recounts his discovery that a company wanted the right to drill for natural gas near his house in Milanville, Pennsylvania, and that they were willing to pay a good amount of money. For the first part of the film, he talked about his home and what he knew about the process of fracking. Then he went on an odyssey across the United States to see what the effects of it have been. Finally, he returns home with his newfound information, and decides that he would rather not allow any fracking. At the same time, he explains the potential consequences of the practice for his region of the world, which includes the New York City metropolitan area. There was even a moment about twenty minutes before the end when he was done with his journeys and got a phone call about some test results he had commissioned earlier, in the first act of the film.