Three-act structure is the general formula for most stories, especially in film. David Mamet summed it up pretty well in a book I’m going to be referencing a few times: Three Uses of the Knife. Boy meets girl. Boy loses girl. Boy gets girl.
I’ll note that a happy ending is not mandatory. Nor is any romantic plot required, though it is somewhat typical.
It mirrors some aspects of life conveniently, and can provide a spine for many biopics. If you’re trying to turn someone’s career into a film, you can always feature their first assignment, their greatest assignment and their last assignment. This has worked since long before Beowulf.
If you’re doing the story of a celebrity, show the main character before he was famous. Then when he deals with fame. And end it with the protagonist either as an elder statesman like Johnny Cash in Walk the Line, a has-been like Jake Lamotta in Raging Bull a tragic figure with an unfortunate death as in Selina, or a tragic figure with another dark fate as with Howard Hughes in the Aviator.
If the story is about an incident, rather than a lifetime, a three part approach still works, as all stories have a beginning, middle and end. The middle part is usually half the film, but the beginning and end usually receive a disproportionate amount of time in terms of the amount of time it’s supposed to cover. It does get a bit more complicated than just that.
There’s a particular way to put all of this together, that works for films in any genre. One problem is that it can make the basic plot of a film rather predictable if the trailer reveals too much information.
There’s a partial explanation of this in the Prestige, as the rules of a magic trick could just as easily apply to the rules of storytelling, which is something that Christopher Nolan is well-aware of.