I was watching a you-tube video of a screenwriter talking about writing and he said .. start your story later than you think and end your story earlier than you think, and everything else goes in the middle.
Aristotle's 3 act structure is the popular understanding of story structure. Any child understands what a beginning, middle and end to a story is. The story starts, the story ends, and in between, well, that's the middle.
That's what we commonly understand when we watch a film, the first 20 to 35 mins is the beginning, the middle 40 to 60 mins is the middle and the last 20 to 35 mins is the end. We get that we learn about a problem or conflict, it builds, becomes more complicated, comes to a head, resolves and the film ends.
A problem is set, the protagonist has to solve that problem, there are lots of obstacles, things happen that we couldn't imagine happen happen, we go on a journey and live the story out with the character(s) for better of for worse, we see then transform all the way to the bitter or sweet end. These moments that I describe vaguely here are known as key moments in a film, plot points/ turning points, mid point, inciting incident and the climax.
Every film rests within the tension and resolution of some sort of problem, this problem, takes the protagonist out of their ordinary life, into the world of the film and it ends (more often than not) in them resolving the problem and being able to return to their life once more. It reflects the viewer's journey, they have 'left their ordinary life' at the box office door and will return to it once the film has ended, and during their time watching the film, they hope to have a purge of emotion, or catharsis, by experiencing the hero's journey.
We can probably see that the way these points occur link the film together, so that the action of the film is being constantly moved forwards by the consequences or the necessity of what has already happened.
