(CNN) -- Last week's attempted terror attack on an airplane heading from Amsterdam to Detroit has given rise to a bunch of familiar questions.

How did the explosives get past security screening? What steps could be taken to avert similar attacks? Why wasn't there an air marshal on the flight? And, predictably, government officials have rushed to institute new safety measures to close holes in the system exposed by the incident.

Reviewing what happened is important, but a lot of the discussion is off-base, a reflection of the fundamentally wrong conception most people have of terrorism and how to combat it.

Terrorism is rare, far rarer than many people think. It's rare because very few people want to commit acts of terrorism, and executing a terrorist plot is much harder than television makes it appear.

The best defenses against terrorism are largely invisible: investigation, intelligence, and emergency response. But even these are less effective at keeping us safe than our social and political policies, both at home and abroad. However, our elected leaders don't think this way: They are far more likely to implement security theater against movie-plot threats.

A "movie-plot threat" is an overly specific attack scenario. Whether it's terrorists with crop dusters, terrorists contaminating the milk supply, or terrorists attacking the Olympics, specific stories affect our emotions more intensely than mere data does.