The official U.S. approval of a coronavirus vaccine for elementary school students removes one of the last barriers to ending the pandemic, but it’s obvious that a significant portion of the country will never fully embrace vaccination. We’ve tried just about every form of positive motivation, including emphasizing family reunions, giving away beer and dangling $5 million in lottery winnings — with mixed results. For example, researchers found that Ohio’s distinctive lottery program didn’t actually affect vaccination rates.

To combat vaccine hesitancy, we need to grasp its psychological roots. Alongside skepticism of institutions and experts, exposure to misinformation, and other often-cited reasons for resisting vaccines sits a clear emotional explanation: Many people are afraid that they’ll make a bad decision. They’re influenced by the psychology of anticipated regret. Understanding this reaction can help us get more shots into arms, removing one of the final obstacles to controlling the virus.

It’s widely understood that when humans make decisions, they engage in a cost-benefit analysis. But psychologists have shown that people also conduct a less-rational calculation involving the regret they might experience. When deciding which of two roads to go down, they not only consider the statistical probabilities but also implicitly imagine their reactions to worst-case scenarios. In these analyses, potential bad outcomes weigh heavier on the mind than equally likely positive possibilities.

When do people anticipate feeling the most regret? When outcomes will derive from actions they take (as opposed to the consequences of declining to act), research shows. Psychologists — notably Daniel Kahneman, who won a Nobel Prize in economics for his work on decision-making — have demonstrated these tendencies in a series of experiments. For example, Kahneman found that people anticipate feeling more regret if they were to lose money by switching to a new stock vs. taking a loss on their current stock. And this regret is maximally intensified when we freely choose to take action — we are not ordered or coerced — and when it involves new or experimental activities. For example, Kahneman found that people anticipate more regret when imagining an accident that occurs while driving home along a new route compared with driving on one’s normal route. Anticipated regret is why people often prefer to stand still rather than move forward.

Anticipated regret sheds light on why vaccine-hesitant people seem more comfortable taking their chances with the virus rather than getting the shot, a decision that is not rational given the relative likelihood of experiencing severe effects of covid-19 vs. severe vaccine side effects. When a person becomes infected with a virus and contracts a disease, it is something that happens to them; it is not — so the mind tells itself — the result of an active decision. (Self-optimism is another widespread psychological trait; most people assume that they won’t get infected in the first place and that even if they do, they’ll be fine.)

Now let’s imagine someone who decides to get vaccinated and suffers some sort of severe side effect or reaction. There’s no evading that it was her choice to get the vaccine. As a result, she has only herself to blame (or so she might conclude) — no matter how rare the side effects are. (Some evidence suggests that the aversion to making a decision that could lead to a bad outcome is especially strong in the medical context.)

Vaccines are no longer experimental, but the coronavirus vaccines do involve a new technology. That probably intensifies the imagined potential regret in the minds of people thinking about side effects. Indeed, the psychology of anticipated regret may help explain the skewed view of risk among the vaccine hesitant: In a Yahoo News-YouGov poll this summer, just 29 percent of unvaccinated Americans said they thought covid-19 was a bigger threat than the vaccine.

It’s not all bad news, however: The psychology of regret can also help explain why coronavirus vaccine mandates have generally been so effective. Despite the many assertions that mandates would lead to mass resignations, the employees of many organizations ultimately got on board. Consider New York City’s largest police union, which fought such mandates in court and argued that the police department would lose thousands of officers. In the end, out of a force of about 35,000 officers, fewer than three dozen refused the vaccine. Similarly, of the 67,000 employees at United Airlines facing a mandate, only 320 refused to get vaccinated.

The collapse of resistance to the mandates, following fierce pledges to quit, is puzzling until you consider the psychology of regret. When people don’t feel the weight of making their own choice, they aren’t as tormented by the anticipated negative outcomes of their decision. Mandates externalize responsibility for getting vaccinated — shifting it from the self to others — making it easier to go forward with getting a shot. (Confronting the reality of losing a job surely also has a persuasive effect.)

Strict mandates alone aren’t enough. I teach a concept I call empathic firmness: When we, as leaders, need to impose a strict policy, we also must keep addressing the concerns of policy resistors — in this case, working to make people who are wary of vaccines more comfortable with complying with the mandates. When people sense that those enforcing a policy are listening to them, they are less likely to shut down. It is easier, however, to empathize with the holdouts if we understand the psychological forces influencing them. If widespread vaccine mandates are implemented with empathic firmness, we can all anticipate a little less regret in the future.