The authors called this effect “ego depletion” and said it revealed a fundamental fact about the human mind: We all have a limited supply of willpower, and it decreases with overuse. Eating a radish when you’re surrounded by fresh-baked cookies represents an epic feat of self-denial, and one that really wears you out. Willpower, argued Baumeister and Tice, draws down mental energy—it’s a muscle that can be exercised to exhaustion.

Nearly 20 years ago, psychologists Roy Baumeister and Dianne Tice, a married couple at Case Western Reserve University, devised a foundational experiment on self-control. “Chocolate chip cookies were baked in the room in a small oven,” they wrote in a paper that has been cited more than 3,000 times. “As a result, the laboratory was filled with the delicious aroma of fresh chocolate and baking.”

In the history of psychology, there has never been a more important chocolate-y aroma.

Here’s how that experiment worked. Baumeister and Tice stacked their fresh-baked cookies on a plate, beside a bowl of red and white radishes, and brought in a parade of student volunteers. They told some of the students to hang out for a while unattended, eating only from the bowl of radishes, while another group ate only cookies. Afterward, each volunteer tried to solve a puzzle, one that was designed to be impossible to complete.

Baumeister and Tice timed the students in the puzzle task, to see how long it took them to give up. They found that the ones who’d eaten chocolate chip cookies kept working on the puzzle for 19 minutes, on average—about as long as people in a control condition who hadn’t snacked at all. The group of kids who noshed on radishes flubbed the puzzle test. They lasted just eight minutes before they quit in frustration.

The authors called this effect “ego depletion” and said it revealed a fundamental fact about the human mind: We all have a limited supply of willpower, and it decreases with overuse. Eating a radish when you’re surrounded by fresh-baked cookies represents an epic feat of self-denial, and one that really wears you out. Willpower, argued Baumeister and Tice, draws down mental energy—it’s a muscle that can be exercised to exhaustion.

That simple idea—perhaps intuitive for nonscientists, but revolutionary in the field—turned into a research juggernaut. In the years that followed, Baumeister and Tice’s lab, as well as dozens of others, published scores of studies using similar procedures. First, the scientists would deplete subjects’ willpower with a task that requires self-control: don’t eat chocolate chip cookies, watch this sad movie but don’t react at all. Then, a few minutes later, they’d test them with a puzzle, a game, or something else that requires mental effort.

Psychologists discovered that lots of different tasks could drain a person’s energy and leave them cognitively depleted. Poverty-stricken day laborers in rural India might wear themselves out simply by deciding whether to purchase a bar of soap. Dogs might waste their willpower by holding back from eating chow. White people might lose mental strength when they tried to talk about racial politics with a black scientist. In 2010, a group of researchers led by Martin Hagger put out a meta-analysis of the field—a study of published studies—to find out whether this sort of research could be trusted. Using data from 83 studies and 198 separate experiments, Hagger’s team confirmed the main result. “Ego depletion” seemed to be a real and reliable phenomenon.

In 2011, Baumeister and John Tierney of the New York Times published a science-cum-self-help book based around this research. Their best-seller, Willpower: Rediscovering the Greatest Human Strength, advised readers on how the science of ego depletion could be put to use. A glass of lemonade that’s been sweetened with real sugar, they said, could help replenish someone’s inner store of self-control. And if willpower works like a muscle, then regular exercise could boost its strength. You could literally build character, Baumeister said in an interview with the Templeton Foundation, a religiously inclined science-funding organization that has given him about $1 million in grants. By that point, he told the Atlantic, the effects that he’d first begun to study in the late 1990s were established fact: “They’ve been replicated and extended in many different laboratories, so I am confident they are real,” he said.

But that story is about to change. A paper now in press, and due to publish next month in the journal Perspectives on Psychological Science, describes a massive effort to reproduce the main effect that underlies this work. Comprising more than 2,000 subjects tested at two-dozen different labs on several continents, the study found exactly nothing. A zero-effect for ego depletion: No sign that the human will works as it’s been described, or that these hundreds of studies amount to very much at all.

This isn’t the first time that an idea in psychology has been challenged—not by a long shot. A “reproducibility crisis” in psychology, and in many other fields, has now been well-established. A study out last summer tried to replicate 100 psychology experiments one-for-one and found that just 40 percent of those replications were successful. A critique of that study just appeared last week, claiming that the original authors made statistical errors—but that critique has itself been attacked formisconstruing facts, ignoring evidence, and indulging in some wishful thinking.

For scientists and science journalists, this back and forth is worrying. We’d like to think that a published study has more than even odds of being true. The new study of ego depletion has much higher stakes: Instead of warning us that any single piece of research might be unreliable, the new paper casts a shadow on a fully-formedresearch literature. Or, to put it another way: It takes aim not at the single paper but at the Big Idea.

Baumeister’s theory of willpower, and his clever means of testing it, have been borne out again and again in empirical studies. The effect has been recreated in hundreds of different ways, and the underlying concept has been verified via meta-analysis. It’s not some crazy new idea, wobbling on a pile of flimsy data; it’s a sturdy edifice of knowledge, built over many years from solid bricks.

And yet, it now appears that ego depletion could be completely bogus, that its foundation might be made of rotted-out materials. That means an entire field of study—and significant portions of certain scientists’ careers—could be resting on a false premise. If something this well-established could fall apart, then what’s next? That’s not just worrying. It’s terrifying.

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