Water from Addicks Reservoir flows into Houston neighborhoods as floodwaters from Tropical Storm Harvey rise in 2017. Associated Press/David J. Phillip, File

Hurricane Harvey flooded Houston in August 2017, forcing tens of thousands of people out of their homes and stranding others on roofs and porches. Millions watched the disaster unfold on their television screens, but one group sprang into action. The “Cajun Navy” – boat owners from Louisiana, many of whom had endured the ravages of Hurricane Katrina – hitched all manner of watercraft (bass boats, air boats) to their vehicles, drove to Texas and set about rescuing thousands of residents. The informal group, which coordinates using social media, has also traveled to North Carolina and Florida to help flood victims.

Why do some people feel compassion, and act, when they hear about mass human suffering, while others put the distress out of their minds and go back to their daily business? The question has long drawn the attention of psychologists and philosophers, not to mention activists looking for ways to get people off their sofas (or to open their wallets) when tragedy strikes – or when governments commit unethical acts.

In the case of the Cajun Navy, one easy answer might be that its members were primed to act because, as Katrina survivors, they had experienced a blow like that endured by Harvey’s victims. Shared pain, the argument goes, insulated them from some of the “bugs” of human compassion, notably the tendency to be moved deeply by a single, identifiable victim (a man or woman drowning) but to respond more blandly as the scale of a tragedy grows (a city underwater).

But as a method for increasing compassion, empathy-through-adversity is a highly unsatisfying solution, since it means that the way to warm people’s hearts is to make them suffer first. Fortunately, shared pain, by itself, isn’t what makes the difference, according to new research from my lab, led by Daniel Lim. More specifically, people who have undergone adversity have a greater sense of efficacy when it comes to helping others. Through their own harsh experiences, they’ve come to believe that even small acts of kindness have an impact on those in need. “The best way you can thank somebody for helping you is to go help somebody else,” an engineer and Cajun Navy member named Ben Theriot told the New York Times during Harvey.

As luck would have it, we can disentangle these two factors. To help people become more compassionate, we can convince them that their efforts to aid others can make a difference, as opposed to waiting for them to be struck by adversity. The research suggests that doing so will make them more willing to lend a hand in a crisis.

Our initial investigation found that past experience with adversity does have positive effects on compassion, without pinning down the mechanism. (It’s not self-evident that this would be the case: An alternative hypothesis would be that adversity hardens the heart.) In one study, we asked more than 200 subjects about the severity of hardships they’d faced – loss of loved ones, serious illness, violence or similar tragic occurrences – and measured their compassion through their level of agreement with statements like, “It’s important to take care of people who are vulnerable.” People who had experienced adversity expressed more compassion than those who hadn’t (as reflected in survey answers), were more willing to donate to the Red Cross at the end of the study, and were more willing to help complete tasks for someone else in the lab (an actor) who reported feeling ill.

Importantly, the type of adversity people had experienced didn’t seem to matter: Someone who had been afflicted with a health crisis was as likely to feel compassion for another person living through the aftermath of a natural disaster as they were for someone facing health problems.

More recently, we zeroed in on whether past adversity helps to counteract the failure of compassion to grow as the scale of a tragedy increases, a tendency called “compassion fade” that is well established in the psychological literature and that is famously captured by a saying often attributed to Stalin: “One death is a tragedy. A million deaths is just a statistic.” In several experiments involving hundreds of participants, we presented people with images of, and information about, a single child suffering as a result of the conflict in Darfur – or eight children. We also asked those people about personal crises they’d faced. Those who had experienced little or no adversity in life reacted to the two presentations roughly equally, but those who had faced significant adversity (the top third of the sample) expressed levels of compassionate concern that were about 20 percent greater when the number of suffering children rose.

Compassion may shut down as tragedy expands because people feel overwhelmed and helpless, so we wondered whether people who had experienced more adversity in life might be more convinced that their altruistic acts are effective. In our experiments, we specifically asked people if they thought they could make a difference in the lives of the Sudanese children. As expected, those who had experienced greater adversity reported a stronger belief that even small actions could matter. Moreover, this belief directly predicted how much compassion they felt – and, when we gave them the opportunity, how much more money they were willing to donate to charities like UNICEF to help such children. In fact, those who had experienced adversity gave more than double the amount of their low-adversity peers.

To be certain that belief about efficacy was the ingredient that mattered, we intervened, in a study involving 98 participants, to change people’s views on that question. We administered a bogus empathy test to people who had little experience of adversity in their lives and told them that the results revealed they were “good at caring for others and … more successful in alleviating their pain.” That false feedback changed their self-reported belief in the effectiveness of their actions; it also changed their reactions as the number of suffering Darfur children grew. Now the low-adversity group, too – just like those who had gone through tough times – grew more concerned when there were more victims.

The upshot is straightforward but profound. Yes, those who have faced adversity in life are more immune to the pernicious compassion fade that plagues the human response to mass suffering – the impulse to weep over a photo of a Salvadoran father and daughter who died attempting to cross the Rio Grande, for example, but to tune out news stories about the mistreatment of thousands of people in border facilities.

But it’s not suffering per se that produces this immunity: It’s that those who experience hardship come to believe that even small actions like donating modest sums, or offering to listen or to help even one victim, can make a difference for people in distress. And that should give us hope, because if that belief is adopted by enough people, the resources needed to address problems at larger scales will start to flow.

The best way to change people’s minds on this question, of course, isn’t through providing false feedback, as we did in our experiment, but rather by offering opportunities to witness firsthand, and, better yet, experience, the power of helping. Both those who receive assistance during personal crises and natural disasters, and those who give it, palpably perceive its effectiveness. Whether through encouraging volunteerism, or having volunteers spread the word that even small acts of compassion can have a large collective impact, giving people a sense of empowerment in the face of tragedy will help reduce their tendency to turn away. Simply watching others help on television isn’t enough; people need to see altruism up close in order to become convinced of its efficacy.

People who have suffered do possess wisdom that lets them overcome the paralysis produced by compassion fade – but fortunately, that wisdom is available to all of us.