In a new essay, Malcolm Gladwell offers an explanation of how school shootings “catch on.” School shootings, as we know them, took off in the late 90s. Between 1996 and 1999 there were eight major attacks, culminating in the Columbine slaughter in Littleton, Colorado in April 1999. The Sandy Hook Elementary School shooting was less than three years ago—December 2012—but in that short span, we’ve already seen more than 140 attacks. School shootings are perhaps the most bizarre, inexplicable phenomenon of modern American life. After the Oregon shooting earlier this month, President Obama remarked, “Somehow this has become routine.”
Gladwell tries to make sense of the epidemic by consulting a study of riots by Stanford sociologist Mark Granovetter. Granovetter sought to understand “why people do things that are at odds with who they are or what they think is right”—for instance, why typically non-violent, law-abiding people join a riot. He concluded that people’s likelihood of joining is determined by the number of people already involved. The ones who start a riot don’t need anyone else to model this behavior for them; they have a “threshold” of zero. But others will riot only if someone else has initiated it; they have a threshold of one. Some need to see two people to be convinced; others need to see three or five or, at the farthest end of the spectrum, the entire society.