TL;DR. Repetition isn't a flaw you varied your way out of, it's how you teach an audience the rules of your story, and an audience that knows the rules can run ahead of you, which is why they lean in. The first version has to play completely straight, because you can't return to something nobody saw plain. Every return after that changes one value and raises the cost, never the volume, and a return doesn't have to be the whole scene again. Then you break the pattern once, at the moment it hurts your character most.

Why does repetition work on an audience at all?

Audiences are prediction machines. They build a model of your story while they watch it, and much of what they experience as pleasure is that model turning out to be right. David Huron's Sweet Anticipation, MIT Press, 2006, argues this about music: expectation is built from what's already happened, and the reward comes from predicting accurately, which is also what makes a violation land. Nobody can anticipate anything until it has happened twice.

That's what writers give away when they vary the second pass into unrecognizability. They were worried about boring the reader, so they removed the one thing that could have put the reader ahead of the story. Boredom isn't caused by recognition, it's caused by recognition that costs nobody anything.

Is it a motif, a runner, or a structural loop?

These three get confused constantly, and they're governed by different rules.

A motif is a small unit that returns with a new value attached. In Casablanca, written by Julius J. Epstein, Philip G. Epstein and Howard Koch, Michael Curtiz directing, "Here's looking at you, kid" appears four times and means something different each time. Same with the song. Ilsa says "Play it, Sam. Play 'As Time Goes By'" over Rick's standing order never to perform it, and later Rick tells Sam, "You played it for her, you can play it for me." The words barely move. The man saying them has.

A runner is a repeated bit the audience is allowed to expect and enjoy, and its job is tone and rhythm, not structure. Runners pay in recognition, and they can be converted into something serious once, which is the most efficient trick in comedy.

A structural loop is when the return is the architecture rather than an ornament. Groundhog Day, Run Lola Run, Edge of Tomorrow. Here the rules you teach in the first pass become the contract you're going to break in the last one. If you don't know which of the three you're writing you'll apply the wrong fix, because motifs die from too much change and loops die from too little.

Why does the first version have to play straight?

Groundhog Day was written by Danny Rubin and Harold Ramis, Ramis directed. Rubin's original draft began with Phil already caught in the loop, opening on the "I Got You Babe" wake-up, and Ramis liked starting in the middle. In development the beginning kept creeping backward. The suggestion to start before the loop, so the audience could watch Phil's first reaction, came from associate producer Whitney White, and the news-station opening was added later during reshoots. The finished film opens on February 1 in Pittsburgh and then plays February 2 once, start to finish, before anyone knows it's a pattern.

That creeping backward is the most common note I'd give on a loop script. You can't repeat something the audience never saw plain. The straight version is the baseline they'll measure every later return against, and it's the only pass where you get to be boring on purpose.

How much changes on each return, and how does the cost go up?

One value, and the cost rises by relocation rather than amplification.

Run Lola Run, written and directed by Tom Tykwer, is eighty minutes and three attempts at the same twenty. The hinge is a man with a dog on the stairs. First run, Lola goes past him. Second run, he trips her, she's late to the bank, she overhears a different sentence from her father's mistress, and she ends up robbing her own father at gunpoint. Third run, she jumps him, arrives earlier, and the bank sequence dissolves because her father has already left with a customer. One man and one dog, and the runs end with different people dead.

Whiplash, written and directed by Damien Chazelle, is the escalation lesson. In the first ensemble rehearsal Fletcher throws a chair at Andrew over the tempo on Hank Levy's "Whiplash," then slaps his face repeatedly. If the film kept doing that it would be dead by the second reel. Instead it relocates the damage, out of the rehearsal room and into Andrew's relationship with Nicole and his family's table, and finally, at the festival, Fletcher counts the band into "Upswingin'" by Tim Simonec, a chart Andrew has never seen and has no music for. Same relationship every time, new thing to lose, and Fletcher never throws a bigger chair.

Does a return have to be the whole scene again?

No, and most of the good ones aren't. Five ways around it.

Hand it to a different witness. Rashomon, 1950, screenplay by Akira Kurosawa and Shinobu Hashimoto, Kurosawa directing, gives the same crime four times, through the bandit Tajomaru, the wife, the dead samurai speaking through a medium, and the woodcutter. The event never changes. The information does, and so does what each telling reveals about the teller.

Fragment it. Edge of Tomorrow, screenplay by Christopher McQuarrie, Jez Butterworth and John-Henry Butterworth, Doug Liman directing, keeps shortening its resets until a death is a cut. Justin Chang in Variety credited the writers, "with the assistance of the editors," for "breezy narrative shorthand." By the back half one line restores the whole beat, because the audience already learned it.

Let somebody report it. A return described by a character who wasn't there carries their error with it.

Put an object in for the scene. In Up, screenplay by Bob Peterson and Pete Docter, Docter directing, the bottle cap Ellie pinned on Carl as a kid comes back when Carl pins it on Russell and calls it the Ellie Badge, and her scrapbook comes back with the blank pages filled in. The object does what the scene would have taken four minutes to do.

Run it backwards once, and let the character who always asks be the one answering.

How do you chart returns and intervals in a real draft, and where does this fail?

Make one column per repeated element. Down the rows, the page number of each appearance, in one phrase what changed, and in one phrase what it cost somebody. Then look at the gaps between page numbers, because that's your tempo and you chose it whether you meant to or not. Three returns across ninety pages is a motif. Three across fifteen is a drumbeat.

Three failure modes show up in that chart immediately. A column where the cost phrase is blank or identical twice is a rerun, so cut one. A column where the "what changed" phrase runs long is a column where you changed so much it stopped being a return. And returns clustered in the first act with nothing after page sixty means you taught the audience a rule you never collected on, which is the quietest version of this mistake and the hardest to see from inside your own draft.

Then break the pattern where it costs the most. You've spent the script teaching the audience what comes next, and you get to spend that once, at the worst possible moment for your character.

Before you call it a return, run this checklist

Did I ever play this beat completely straight, with nothing withheld, before I started varying it?

On each return, can I name the one value that changed in a single phrase?

Is the second pass more expensive for somebody than the first, and the third more than the second?

Am I raising the cost by relocating the damage, or just by making the same thing louder?

Have I written the page numbers down and looked at the gaps, or am I guessing at tempo?

Could this return be a fragment, a report, a different witness or an object instead of the whole scene?

Do I know whether I'm writing a motif, a runner or a structural loop, and am I applying that one's rules?

Where does the pattern break, and is that the single worst moment for the character who built it?

Repetition is a loan of attention that the audience extends you cheaply and expects back with interest. Go pull up every scene in your draft that returns to something, write the cost in the margin of each one, and if the second margin note isn't bigger than the first, cut the second scene and spend the pages on the break instead.

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Sources. Credits and plot details for Groundhog Day, Whiplash, Run Lola Run, Rashomon, Edge of Tomorrow, Casablanca and Up are from the respective Wikipedia entries, including Hank Levy's "Whiplash" and Tim Simonec's "Upswingin'," the four accounts in Rashomon, Justin Chang's Variety line on narrative shorthand, the four uses of "Here's looking at you, kid," and the bottle cap and scrapbook in Up. The Groundhog Day development account, Danny Rubin's original mid-loop draft, associate producer Whitney White's suggestion to begin before the loop, and the reshot news-station opening, comes from Wikipedia and from No Film School's 2016 piece on the script's path to production. The argument about prediction and expectation is from David Huron, Sweet Anticipation: Music and the Psychology of Expectation, MIT Press, 2006.