First "3 Act" is about structure, not story. Secondly, "3 Act" is not a formula. Everything has a beginning and an end ("2 Act"). If you consider the action in the middle, you have "3 Act"--beginning, middle and end. The problem that arises is that structure and story have become superimposed by many screenwriting proponents. The merger of the "Hero's Journey" with the UCLA statistical model has led to an obsession with "beats" and "events". Commonsense tells us that by the middle of the movie, we should be reaching a point where things are going to come to a resolution. I like to think of movies as rollercoasters. Good rollercoasters often have that final joyful kick before the conclusion.
So taking rollercoasters, I know it starts off slow and builds, in the middle is the action, and then things heat up for the final thrill before pulling back into the station--beginning, middle, end ("3 Acts"). After that first hill, there's the stomach drop ("transition"). Before the final slowdown, there's the kicker ("denouement/do-or-die moment"). That's it. If you don't have a beginning, middle and end, you don't have a movie. Period.
Snyder, Hauge and others draw upon the fact that most stories follow the Hero's Journey. The Hero's Journey is NOT the only way of telling a story. It is a common western motif, though not necessarily true in Asian or Native American cultures. In fact, it is often male-biased. Reading about female heroes provides different strategies than slaying the dragon. Nonetheless, the Hero's Journey (which is rather formulaic) is often characterized by six steps: (1) the hero is called but resists, (2) the hero is forced to start his quest, (3) the hero meets the dragon who defeats him, (4) he meets a mentor who heals/trains him, (5) the challenge has now greatly increased, and (6) the hero conquers the dragon. There are other finer points one can add. Now "six" is divisible by "3", so many gurus divide this up. Act One: you must introduce the hero and start him on his quest. That quest challenge is the first hoop and introduces the second act. Act Two: Hero confronts the antagonist and must confront his own flaws with the help of others. This leads to the second hoop, the "impossible challenge" that ushers in the third act. Act Three: the hero is confronted and almost loses himself but transcends his limitations for that final desperate action which overcomes his flaws and the villain. There is the ever after (usually happy but not necessarily) where the world is changed. That "story formula" has become linked to "structure" which is unfortunate.
There are non-linear ways of telling stories. There are non-hero journey stories. Comedies often don't fit neatly into this paradigm. There, events spiral out of control. The question is does a protagonist need to be a "hero" or can they be acted upon? Was Chauncey Gardener in "Being there" a classical hero? Still, it falls into the model because he's forced out of his comfort zone. For many people, they want action and a hero, so that fits in well with the HJ formula. Implicit in this model is conflict resolution. Sometimes the protagonist is a "martyr", the villain is death--"Brian's Song", "Love Story", "Titanic", "Buried", etc.
Structure for television, the "acts", is very precisely defined to allow for commercial breaks. Each "act" ends with a hook to draw the audience back. Television often has a "six act" structure--teaser, act 1, act 2, act 3, act 4 and tag. However, television's use of the HJ formula is less forced since it has three or more arcs that are ongoing--episode, season, and series. Here the acts continue to serve to organize the presentation. Act 1 - What's the episode about?, Act 2 - What's the conflict?, Act 3 - What's the flipside?, and Act 4 - The Negotiation. The teaser is, well, the teaser. The tag is the outcome.
New writers benefit from having a clean model to follow. And I really encourage new writers to master this before trying to "break the rules". You can't break the rules until you know what they are and have mastered them. Once you've written a couple scripts using this approach, you can explore being creative. Like a coloring book, it's okay to color outside the lines but it will look like crap. Once you can color inside the lines, it looks cookie cutter. The next step is drawing your own lines. It will look like crap. But with practice, you should get some art that looks fairly decent. Many of us copy cartoons, manga, etc. These imitations help us develop skills to craft our own cartoon and manga characters by learning styles and proportions. Scripts are the same. The first few are "formulaic" but you're learning structure, format, pacing and other nuances. After five or so, things suddenly come together.
