Pick a film, any film.  If the notion that there are only seven stories (or however many) in the world is correct, we should be able to reverse engineer its specifics and find its template. 

The film I’ve chosen is Guy X.  The story goes something like this:

An American soldier is transported to a military base in Greenland, where he is mistaken for the press office they’re expecting.  The fact that it’s the wrong guy entirely matters not a jot: military intelligence being what it is, our hero is declared press officer whether he likes it or not.

Problem being, there is pretty much zero news to report from the Greenland base.  There are swarms of midges, troops enacting rituals hundreds of miles away from any context where they might have meaning, and that’s pretty much it.  Except for this one cute woman who’s also on the base, and attracts our hero’s attention.  Only, she’s caught up in the world of the commander of this crazy outfit, and rank counts for a lot in set-ups like this.

Taking to his press officer role if only to give himself something to do, our hero starts to get suspicious about what’s going on at the base, and discovers a hidden hospital ward, full of seriously injured soldiers who were hurt at an earlier point of the commander’s inglorious career.  He has exploited the inane system he works in to do what he can to hide his mistake.

But hey, it all works out fine in the end.  Our hero blows the whistle on the commander’s sick exploits, and the story ends with the hero and his new chums flying away from Greenland under newly assumed identities, knowing that the clumsy system they’re part of will never discover what’s going on.

So, there are a few things going on here.  And if you want to reduce the film to its vital elements, you can use its blueprint to create a fairy story.  Like this:

A humble peasant is mistaken for a librarian by the king’s courtiers, and gets to live in the crazy world of the court.  Everything revolves around the assumption that the king is a good and wise man.  But the peasant, smitten by the king’s daughter, discovers the terrible truth about the monarch.  The king is overthrown (overthrone???)  and the peasant and princess head away on horseback using forged papers to start a new life of their own.

Simple, huh?  (And I hope it urges you to see Guy X, which I am very fond of, and was criminally ignored when it was briefly in the cinemas about three years back.)  Now let’s see if we can make things simpler still.  Hmm.  Do that, and the core story starts to look like The Emperor’s New Clothes, in contemporary American military drag, part of a film lineage including M*A*S*H, Dr Strangelove, and Three Kings. 

Maybe we haven’t gone back as far as deducing which of seven ur-stories is Guy X’s ancestor, but this reductionism thing can be taken too far.  What’s useful is looking at the structure and themes of a story, finding precedents for it in film and myth, and seeing how they can usefully shape the way you want to write your own screenplay.