Each of the attacks in Paris that killed 17 people last week was an atrocity, a threat to freedom and an act of terrorism. On those points, most people agree, and they’re right. Most people also fear this marks the beginning of a rash of extremist violence in the West. On that, they’re probably wrong.

If we have learned anything from the experience since 9/11, it’s that the public and its leaders chronically overestimate the danger posed by Islamic militants. This latest episode fits that pattern.