On Monday, just hours after the arrest of a man accused of setting off an explosion in an underground walkway in midtown Manhattan, former New York City police commissioner Howard Safir responded with a message that was both sobering and resolute. “We’re going to be faced with this in the future,” he said on CNN. “We’re New Yorkers. We’ve got to go about our lives.”

Twitter users in New York and beyond echoed his sentiment, noting how the attack — in which three people and the bomber were injured but no one died — scarcely seemed to register for many city residents. “There is no intimidating or terrorizing New York or New Yorkers,” Matt Braunger tweeted. “Dude blew himself up and barely made the trains late.” Jess McIntosh quoted a news report that New Yorkers were “not particularly panicked, but looking annoyed and aggrieved.” Another Twitter user reported that he had witnessed a train passenger who, in the midst of assuring someone that he was all right, was shushed by another passenger because he was in the quiet car.

Safir wasn’t the only current or former New York official to predict that attacks of terrorism would become increasingly common for residents of the country’s largest city after it experienced its second attack in less than two months. But despite the possibility of more terrorist activity, psychological research suggests that New Yorkers’ resilience isn’t likely to fade.

In New Yorkers’ nonchalant reaction, there is a counterintuitive kernel of good news. Exposure to repeated acts of terrorism may help habituate people to terrorism, effectively defusing its intended psychological effect: a widespread sense of vulnerability and fear in a community. Shared resilience in the face of danger can even promote a greater sense of communal solidarity.

But even though adapting to terrorism may have psychological and political benefits, it comes at a price. That sense of communal solidarity can result in greater xenophobia and intolerance, and promote social divisions. And although habituation means that people carry on as usual regardless of the threat, that doesn’t mean they don’t feel anxiety or paranoia — instead, low-grade stress can itself become normal.

“There is a trade-off when you have a society that becomes accustomed to the idea that there will be terrorism and there’s nothing they can do to stop it,” said Yuval Neria, an Israeli psychologist who is now a professor at Columbia University Medical Center. Countries like Israel, which has experienced long periods of repeated terrorist activity, have provided psychologists with case studies about the effects of chronic terrorism. “These societies are stronger in many ways because they are not easily shaken out of their routines when there is violence,” Neria said. “But there’s also a feeling of hypervigilance, a sense that you can’t really trust the people around you, and that takes a toll both psychologically and socially.”

Research conducted in the aftermath of terrorist attacks has shown that there is usually a spike in the number of people reporting psychological conditions like post-traumatic stress disorder or depression, even if they weren’t directly affected by the attack. A survey carried out in the days after the Sept. 11, 2001, attacks found that 44 percent of people in the national sample had some kind of stress reaction associated with PTSD. Similarly, research conducted in the aftermath of the 2005 terrorist bombings in London’s public transportation system found that 31 percent of Londoners reported significant stress in its immediate aftermath.

In these and other similar cases, however, stress levels soon returned to normal, indicating that the attacks hadn’t caused long-term psychological damage. A study conducted in the months after 9/11 found that the incidence of symptoms related to PTSD among people living in the New York metropolitan area had declined substantially. In London, research found stress levels were much lower seven months later.

There’s other evidence that as terrorism becomes part of the fabric of the everyday, it loses some of its power to disrupt and frighten. Dov Waxman, a professor of political science and Israel studies at Northeastern University, studied the impact of Palestinian terrorism in Israel during the second intifada, an uprising in the early 2000s that led to several years of intense violence. He surveyed other research and found that even though suicide attacks in public places increased from 4 in 2000 to 53 in 2002 and a significant number of Israelis were directly affected by terrorism, rates of anxiety and PTSD remained relatively low, and Israelis’ overall happiness was mostly unaffected. These findings showed that not only are people able to recover from the negative psychological effects of terrorism after a short time, but they are also able to adjust to periods of repeated terrorist activity with surprisingly low levels of psychological damage.

Being able to adapt to terrorism is helpful from a political perspective, Waxman said: “The more we allow ourselves to be terrorized and demoralized by repeated acts of terrorism, the more emboldened the terrorists will be.”

In Israel, part of what enabled this psychological and social resilience to build was simply that the media stopped covering it as intensely, according to Waxman. “Having terrorist events on television constantly, on the front page of the newspaper, is very damaging psychologically,” he said.

This assertion has been borne out in an American context as well: A study conducted in the aftermath of 9/11 found that people who watched several hours of TV per day in the wake of the attacks were more likely to have physical and psychological problems years later — even with no other exposure to trauma. In other words, the sooner attacks fade from the headlines, the more quickly people can return to their everyday lives.

But Waxman and other researchers agreed that exposure to terrorism changes societies and people and might have other health risks that we’re just starting to uncover. Some psychologists have argued that even though the incidence of psychological conditions like PTSD and depression may decline following terrorist attacks — or even level off in cases of repeated terrorism — an everyday sense of fear and anxiety can still have negative physical and mental health effects. A recent study of Israeli adults found that consistent exposure to terror threats could create a higher risk for heart disease among otherwise healthy people.

In his study, Waxman found that repeated attacks of terrorism can create a strong sense of group cohesion. But that can be a double-edged sword: Solidarity can be psychologically helpful, but it can also promote xenophobia and intolerance. According to a 2002 poll, the vast majority of Israeli Jews agreed that the events of the second intifada had strengthened national unity. But other surveys around the same time showed that Israeli Jews increasingly viewed Israeli Arabs as a security threat, and later research suggested that Israeli Arabs — who already faced significant prejudice — were even more likely to be discriminated against in the country’s labor market in the months after the outbreak of the second intifada in the fall of 2000.

In the U.S., repeated attacks of terrorism could create even more division in a country already struggling with intense political and social polarization. “You can adjust to losing your sense of safety,” Neria said. “But the emotional infrastructure of the community changes. There’s less trust, there’s more hostility toward people who are different than you.”