Human cognition does not take place in a social vacuum. When a particular incident is cognitively “available,” it is usually because of social influences. When emotions lead people to probability neglect, the alarm shown by others is highly likely to be playing a role. When citizens fixate on a worst-case scenario, social processes are probably ensuring that they do so.

Obviously both government and the media make some risks appear particularly salient. Return to President George W. Bush's plea: “Imagine those 19 hijackers [involved in the 9/11 attacks] with other weapons and plans, this time armed by Saddam Hussein. It would take one vial, one canister, one crate slipped into this country to bring a day of horror like none we have ever known.” Environmentalists, in and out of government, operate in the same way, focusing public attention on potentially catastrophic harms. Well-organized private groups play a central role in activating public concern. But to say this is to get ahead of the story. Begin with an example.

SNIPERS

In fall 2002, a pair of snipers killed ten people in the Washington, D.C. area. The victims were randomly chosen. They included men and women, young and old, whites and African-Americans. Each of these murders was a tragedy, of course; but the actions of the snipers affected millions of others as well. Many citizens were afraid that they could be next. Fear, sometimes dull and sometimes very sharp, gripped the nation's capital. Behavior changed dramatically.