The What-the-Hell Effect: How One Slip Becomes a Spiral

The plan was no sweets until Friday. Then it's 3pm on Tuesday, there are cookies in the kitchen, and one is gone before the decision finishes loading. The cookie is not the interesting part. The interesting part is the verdict that comes down on the walk back to your desk: the day is blown. And a blown day runs on different rules. Pizza for dinner, and a restart penciled in for Monday. Psychologists call that swerve the what-the-hell effect, and its origin story involves a milkshake.

It also has a twist ending almost nobody quotes. The research, running since the 1970s, tells two stories: one about how real the spiral is, and a second, from researchers who followed dieters out of the lab and into ordinary days, about how optional it turns out to be.

The Milkshake Experiment That Ran Backwards

In 1975, the psychologists Herman and Mack published a study in the Journal of Personality that has been unsettling common sense ever since. Under a sensory-rating cover story, participants were required to drink zero, one, or two milkshakes, and were then given three flavors of ice cream to taste. The tasting was the decoy. The real measure was how much ice cream they ate.

For people not on a diet, appetite behaved. The more milkshake they had been required to drink, the less ice cream they ate afterward. Two milkshakes down, not much room left for dessert.

The dieters ran backwards. Restrained eaters, the study's term for people who chronically diet, ate more ice cream the more milkshake they had first been made to drink. The preload that should have blunted their appetite released it. And the inversion belonged to the dieters alone. Without a diet to break, there was nothing to set off.

"What the Hell, My Diet Is Already Broken"

Herman and Polivy named the pattern in a 1980 book chapter, and the name does most of the explaining. The milkshake had not made the dieters hungry. It had made them fail. Their eating rules had exactly two states, kept and broken, and once the required milkshakes pushed them over the line, they were, in the researchers' description, telling themselves: "what the hell, my diet is already broken so I might as well eat and enjoy for now."

Read that sentence slowly, because the whole spiral is inside it. "Already broken" makes the diet pass or fail, with no middle. "Might as well" closes the day's accounting, so everything after the slip is free. "For now" schedules redemption for later, usually Monday, which is how one cookie buys itself five days of company.

The Slice Only Looked Bigger

You might assume the spiral runs on calories, some bodily threshold past which restraint gives out. A study that held the calories perfectly still says otherwise. In 2010, Polivy, Herman, and Deo fed everyone the same slice of pizza and manipulated only how large it appeared. When their slice merely looked big, restrained eaters tended to eat more cookies afterward, while unrestrained eaters tended to eat less. Same pizza, same calories, opposite directions, all hanging on whether the eater believed a violation had occurred.

The trigger is not the food's energy. It is the food's meaning. Polivy and Herman's 2020 review describes preload experiments with equal calories in which restrained eaters went on to overeat only when the preload was a "forbidden" food. An equal-calorie preload that carried no forbidden meaning set off nothing. The effect even has a physical ceiling.

The What-the-Hell Effect Outside the Kitchen

If this only happened around milkshakes, it would be a curiosity. But the shape shows up wherever people draw bright lines for themselves: budgets abandoned on the 9th of the month, a whole gym membership written off over one missed week. By 1996 the phrase had migrated into goal research, when Winona Cochran and Abraham Tesser titled a book chapter after it and argued that how near you are to a goal, and how the goal is framed, shape what happens to performance after a violation.

Then in 2004, Soman and Cheema showed how expensive the pattern can get. In two experiments in the Journal of Consumer Research, violating a goal left people performing worse afterward than people who had never set a goal at all. Sit with that comparison. The goal was supposed to be scaffolding; broken, it read as rubble. And the mechanism had nothing to do with appetite: these were behavioral goals and performance, not diets and desserts. When a violation is coded as a failure, it produces demotivation and negative emotion, and both leak into whatever you do next.

Then Someone Followed Dieters Into Real Life

Every study so far shares an address. The milkshakes, the pizza slices, the cookies all happened in a lab, mostly with college women, always with the rule and the violation designed by the experimenter. In 2009, Tomiyama and colleagues asked the obvious, unasked question in Psychological Science: does any of this happen on an actual Tuesday? They tracked women hour by hour through two ordinary days, catching real diet violations as they happened and watching what followed.

Breaking a diet did not predict eating more in the following hour. What the data showed instead was a compensation effect rather than a disinhibition effect: real dieters adjusted around a slip instead of unraveling after it. The team also rebuilt the classic trigger in the wild, having women drink a milkshake similar in size and preparation to the lab original, dropped into the middle of a normal day. The women ate no more that day than usual, a mean of 1,410 calories against 1,497 on ordinary days, a difference that was not significant. The very trigger that sets off restrained eaters in the lab did nothing out in the world.

This does not make the lab effect a myth. Tomiyama herself notes it "has been replicated numerous times." The two findings describe the same creature in different habitats. The lab builds the spiral a perfect terrarium: a rigid all-or-nothing limit and a violation you are forced into, with no room to adjust afterward. Ordinary life is looser. The limit has give, the day is long, and the decision after the slip stays open. That is the real headline of all those milkshakes. The slip is an event. The spiral is a choice.

How to Make the Spiral Optional

Put the lab and the field together and you get a design spec. The spiral needs a rigid rule to violate and a verdict to enforce; deny it both.

Draw ranges, not lines. A rule with two states hands every slip the power to end it. A rule with give absorbs the slip and keeps working.

Shrink the violation window. "The day is blown" only makes sense if the day is the unit of account. Make the unit smaller. If the account closes at the next meal, a 3pm cookie has nowhere to spread. Any boundary can serve as a restart, the next hour included, which is the everyday version of the fresh start effect.

Pre-decide the post-slip move. The worst moment to choose your response to a slip is right after one, with the verdict already forming. Decide it now: after a miss, the next scheduled action happens as planned, nothing added, nothing punished. It's the same logic behind streaks designed with slack built in, and the work on self-compassion after a setback explains why tone matters too; the harsh inner voice is exactly the failure-coding Soman and Cheema argued does the damage. Future You is built on the matching premise, that intentions beat deadlines and a missed day is human rather than disqualifying, and it's free on iOS and Android.

Back to the Kitchen

The cookie happened. Somewhere in the next few minutes a verdict will try to come down, wearing the voice of discipline, announcing that the day is blown. You now know where that voice learned its lines: a lab, a required milkshake, a rule with no give in it. Out in the real world, women who broke their diets ate no differently in the hour after, and a lab-sized milkshake dropped into an ordinary day left the day's total where it always was.

The rest of your day follows the sentence you pass on the slip, not the slip itself. Decline to pass one, eat a normal dinner, and the spiral, which was never mandatory, simply fails to happen.