It may not surprise you to learn that healthy, well-fed people in affluent countries are often unhappy and anxious. But it did startle Zbigniew Lipowski when he came to a full realization of this fact. He had emigrated to North America from Dublin, in 1955, and, in the mid-nineteen-sixties, was put in charge of the psychiatry practices at two Montreal hospitals, Royal Victoria and Montreal Neurological. Why, he thought, as he worked there, would so many people living in such good conditions have so much anxiety?

Lipowski was born in Poland and, in 1944, took part in the Warsaw Uprising, a mass revolt against the German Army that left more than two hundred thousand civilians dead. Lipowski, masquerading as a French refugee returning to France, was one of the fortunate few who escaped. “Those two months were the most significant experience of my life,” he would later recall. “The odor of burning flesh was with us day and night. We were bombed and shelled daily, food was very scarce, and water had to be obtained at night from a well some distance away. I was so hungry as to almost hallucinate food.”

North America, however, greeted him with constant abundance and leisure. As he pondered the contrast, Lipowski thought of Buridan’s ass: an apocryphal donkey that finds itself standing between two equally appealing stacks of hay. Unable to decide which to consume, it starves to death. The donkey got its name from Jean Buridan, the nominalist fourteenth-century philosopher and Catholic priest who wrote extensively about free will. Buridan posited that free will could sometimes lead to inaction: an inability to choose due to excess uncertainty and, potentially, excess choice. Buridan’s ass, in turn, became the mascot for that general principle (though no equines of any kind actually appear in Buridan’s writing). For Lipowski, this scenario helped to explain the type of anxiety that he was witnessing around him. He called it an approach-approach conflict: faced with enticing options, you find yourself unable to commit to any of them quickly. And even when you do choose, you remain anxious about the opportunities that you may have lost: maybe that other stack of hay tasted sweeter.

Lipowski summarized his theory in a paper published in The American Journal of Psychiatry, in 1970. “I maintain that it is specifically the overabundance of attractive alternatives, aided and abetted by an affluent and increasingly complex society,” he wrote, “that leads to conflict, frustration, unrelieved appetitive tension, more approach tendencies and more conflict—a veritable vicious cycle.” That cycle, in turn, likely had “far-reaching and probably harmful effects on the mental and physical health of affected individuals.” Lipowski concluded that the overabundance of good scenarios was the main source of the anxiety around him. It was here, in the land of plenty, he wrote, “that the fate of Buridan’s ass haunts us.”

While Lipowski’s work received some immediate wide attention, it soon fell into relative obscurity. Thirty years later, the Columbia University psychologist Sheena Iyengar revived the idea of conflict created by an overabundance of choice—a concept that the Swarthmore University psychologist Barry Schwartz would then popularize and rename as the paradox of choice—though, unlike Lipowski, she focussed largely on the concept of cognitive demands. When shoppers had to choose between jams or chocolates, she found, they were more likely to make a selection when faced with six choices than when presented with twenty-four or thirty. They were also more satisfied with their ultimate selection. Too much choice, Iyengar concluded, would reduce motivation. Why exactly that would be the case, however, remained unexplored. One possibility, she hypothesized in her conclusion, was that an abundance of options may “simultaneously attract and repel choice-makers,” an emotion-based explanation not unlike the one that Lipowski had considered. Still, the potential of an underlying emotional tug-of-war remained more speculation than fact.

Around the time that Iyengar and Schwartz were writing, Amitai Shenhav, now a psychologist at Princeton University, began to examine the literature on anxiety—one of the core emotions that people feel when they’re pulled in two directions. As he read, he realized that the nature of the experiences being studied was generally negative by design. “When people study anxious emotional states, they usually use negative stimuli,” he told me. “Like electric shocks: something that makes you anxious because you want to avoid it.” When experimenters looked at choice, on the other hand, they focussed more on the cognitive demands and the results of decisions, not the experience of anxiety as the choice was being made. So, inspired in part by his reading of Lipowski, Shenhav decided to investigate whether making choices from among appealing options could, in itself, provoke anxiety—and whether that anxiety was caused by the sort of emotional back-and-forth that Lipowski had speculated about. “If you think about it, that’s a much more prevalent scenario, when we have to choose between things we experience simultaneously,” he said. “I’ve had intuitions about this my entire life—from decisions like where to go to grad school to where we’re going to go for dinner tonight.”

In a series of imaging studies, Shenhav and Randy Buckner, a cognitive neuroscientist at Harvard, observed students making various choices. One to three days before the actual study began, Shenhav and Buckner had all of the participants evaluate more than three hundred different products, ranging from iPods and digital cameras to water bottles and T-shirts. When the experiment started, participants were put inside an fMRI scanner, shown pictures of the objects, and then asked to indicate which ones they preferred: Would they, for example, like to choose a digital camera or a camcorder? (The participants were told that, at the end of the study, they would randomly receive their object of choice from one of the trials.) Each choice was between either two similarly ranked items—both relatively low-value or both relatively high-value—or two items that were on opposite ends of the spectrum. After they had finished making all of their choices, the participants were asked to rate each decision on a series of five-point scales: How emotionally positive did it make them feel? How anxious did it make them feel? And how certain were they that they had chosen the way they had wanted to? The participants were also offered the surprise opportunity to change their choice: If they had it to do over, would they go the other way?

Unsurprisingly, when people were asked to decide between something like an iPod and a bag of pretzels, they didn’t feel particularly anxious: the choice was clear and life was good. When both choices were low in value, the emotions were similarly clear-cut. No one was particularly happy, but neither were they anxious. But when multiple highly positive options were available—a digital camera and a camcorder, say—anxiety skyrocketed, just as Lipowski had predicted. The choices between those objects that they valued most highly were both the most positive and the most anxiety-filled. The more choices they had—the study was repeated with up to six items per choice—the more anxious they felt. “When you have more good choices, you don’t feel better,” Shenhav says. “You just feel more anxious.”

The neural data that Shenhav and Buckner collected told the same thing. There was a very clear dissociation between the positivity-related and the anxiety-related regions of the brain involved in each choice. In other words, one distinct activation pattern tracked closely with positivity—the value of the good options themselves—while another tracked with the anxiety of making each choice. The activity in the anxiety-related regions, in fact, predicted how likely it was that a person would want to reverse her initial choice. The more difficult the choice was to begin with, the higher the chance of reversal. “It might actually be tracking the conflict after the choice is made,” Shenhav speculates.

Perhaps, then, what we’re really seeing is how the old fear of missing out plays out in the brain. We’re surrounded by great choices to make, great places to be, great things to do—and that’s wonderful. But when we’re made to commit to one, just think of everything that gets away. Shenhav himself refers to it as the “neural correlates of First World problems.” We know that someone else is eating that delicious ice cream that we passed up—or filling that job that we turned down.

Lipowski himself, however, didn’t feel as if the relatively minor scale of the problems that wealthy people face in any way cheapened the emotions felt by his patients. What changes as we move from the scarcity of wartime Warsaw to the abundance of the First World isn’t the nature of the anxiety, it’s just the nature and significance of the choice itself. In one case, it seems heart-wrenching; in the other, trivial. Our brains, though, don’t make those kinds of value judgments: to them, a difficult choice is a difficult choice. And difficult choices mean anxiety.