A classic experiment involved asking people to donate to help hungry children in West Africa. One group was asked to help a seven-year-old girl named Rokia, in the country of Mali. A second was asked to donate to help millions of hungry children. A third was asked to help Rokia but was provided with statistical information that gave them a larger context for her hunger. Not surprisingly, people donated more than twice as much to help Rokia as to help millions of children. But it turned out that even providing background information on African hunger diminished empathy, so people were much less willing to help Rokia when she represented a broader problem. Donors didn’t want to help ease a crisis personi fied by a child; they just wanted to help one person—and to hell with the crisis.

As we all vaguely know, one death is a tragedy, a million deaths is a statistic. As Mother Teresa said, “If I look at the mass, I will never act. If I look at the one, I will.” Professor Slovic calls the first reaction “psychic numbing.” But Slovic wanted to know at what point the number of victims triggers psychic numbing. He set out to find out, and his findings were deeply depressing.

In one of Slovic’s experiments, people were asked to donate to Rokia or, in other cases, to a similar hungry boy, Moussa. In each case, research subjects were quite willing to help and donated generously either to Rokia or to Moussa. But when people were asked to donate to Rokia and Moussa together, with their photographs side by side, donations decreased. Slovic found that our empathy begins to fade when the number of victims reaches just two. As he puts it: “The more who die, the less we care.”

A practical application of these concepts came during the struggle against apartheid in South Africa. The white government there had imprisoned many brave activists, and there was a global campaign focusing on freeing these political prisoners. It never gained traction, however, until the organizers had the idea of refocusing it on an individual and came up with the slogan “Free Mandela!” Once there was a face on the movement, it resonated far more widely—and, ultimately, helped topple apartheid.