The three act structure is the Coca Cola of screenwriting theories. It states that stories have a beginning, a middle and an end. Its simple vagueness allows it to apply to pretty much any story. When people say that the three act model has its flaws, they have a point; when people say that it doesn’t even exist, they’re onto something; when they say that it should be discarded they are very, very wrong.
The three act structure is the only thing a writer can count on an executive knowing about screenwriting. Without it, we’d have no shared language with them. It’s already difficult to get coherent, actionable notes. Without the three act structure, it’d be impossible .
My friend Ben Everhart says: “I personally break Act Two in half — and kinda/sorta think of it as two separate acts unto themselves. But when I speak to producers, I talk in terms of Acts 1/2/3 because that’s the way they evaluate the work. Producers, managers and agents will give you notes based on a Three Act paradigm. You can still use your own method but you need to be able to speak to your colleagues in 3-Act Terms.”
No theory is a magic cure-all. Use whatever model or vocabulary you like in your private life, but know that if you insist on framing everything in terms of five acts, it’s likely to alienate people who don’t know it, as people rarely like or trust new information. You want people to be thinking about your story, not sidetracked on some wonky terminology.
While other approaches wax and wane (Chris Vogler, Blake Snyder, Film Critic Hulk), three act structure has endured. While you won’t always use it to write your story, others will use it to frame their notes, and a good storyteller knows to value communication over pedantic accuracy.