More on the illusion of ‘perfect security’

A quick follow-up to my previous post on the illusion of achieving perfect security against terrorist attack: Today’s NY Times has an op-ed by Clark Kent Ervin, a former State Department official who know heads the Aspen Institute’s Homeland Security program. Ervin makes a number of good points in his piece, but his wrap-up reveals a curious lack of understanding of the basic problem. He writes:

Perhaps the biggest lesson for airline security from the recent incident is that we must overcome our tendency to be reactive. We always seem to be at least one step behind the terrorists. They find one security gap — carrying explosives onto a plane in their shoes, for instance — and we close that one, and then wait for them to exploit another. Why not identify all the vulnerabilities and then address each one before terrorists strike again?"

Sorry, Mr. Ervin, but it is impossible to "identify all the vulnerabilities and address each one" beforehand. That is like asking a football coach to identify all the different ways the other team might try to score, and "address each one." The problem is that the other side can think and plan and innovate too, and develop creative new ways to deal with any security measure we might dream up. In any competitive, strategic interaction, there’s rarely if ever a "last move" and one is sometimes forced to be reactive because the other side takes the initiative in ways we simply didn’t think of. The best we can do is try to make it very hard for terrorists to attack us, which can both protect us directly and force them to take more elaborate measures that in turn makes it easier to find them beforehand. 

But it is a little worrisome to read that a knowledgeable official with lots of experience still thinks it is possible to achieve some sort of perfect defense.