In environmental contamination, a field which I had some practice , enforcing hazardous waste laws for the state of Colorado, this results in a very disproportionate share of our private and government dollars that are devoted to environmental clean up that are being devoted to chasing things down to the last molecule. It's very important to get the first 99 percent of the waste. It's important to get most of that remaining one percent. But, when you're down to 0.001 percent and you are still chasing those very few molecules it gets very expensive to get those last ones out and you may double the cost of the project for essentially no gain at all in actual safety. Now, back to the risk of terrorism.
Terrorism is a sensational event.
When there is a terrorist attack in the United States everybody knows about it within a day at least. And, naturally the things you see on television tend to be the things that people think about the most. There is plenty of studies of how television skews people's perceptions of the world. And the answer is about 10 percent. That is because on T.V. you don't see a lot of happy marriages.