Gustav Freytag derived it from Greek and Shakespearean tragedy in the 1860s, and the shape is a triangle for a reason: it assumes a story that builds to a single peak and then descends. That descent — the falling action — is the part modern structure mostly deleted, which is why the pyramid reads as lopsided against a contemporary film.
It remains the most useful diagram for one specific job: showing a client where the tension in a piece currently sits. Plot a corporate video against it and the usual finding is a long exposition, a climax in the last eight seconds, and no rising action at all. That is a diagnosis you can act on, which is more than "it feels flat" gives you.
Do not use it as a template. As a description of tragedy it is accurate; as a set of instructions it produces stories that peak once and then explain themselves for a third of their runtime.
What are the five parts of Freytag’s pyramid?
Exposition, rising action, climax, falling action, and catastrophe or resolution. The climax sits at the apex and the falling action descends from it.
What is the difference between Freytag’s pyramid and three-act structure?
Freytag gives significant weight to the falling action after the climax, which suits tragedy. Three-act structure resolves quickly after its climax, which suits almost everything made now. The rising half of both is nearly identical.