or most of us, airports are the only places where life has really changed since 9/11. The terminal has become a vast theater of the absurd where aspiring passengers line up halfway back to town. The shoes of little old ladies are gravely removed and inspected. Men in suits take their cell phones out of the bag and put their laptop computers into the bag-no, wait, cell phones in and computers out. Random passengers stand spread-eagle d while strangers say to them softly, 'Now I'm going to run my hands around your waist.

Is that all right?' Somewhere unseen, a food-service worker is assembling plastic knives but metal forks in meals headed for first class. And all the while the public-address system hectors us to 'report any suspicious activity.' Many people, understandably skeptical about these quasi-religious rituals, have stopped flying instead. Others are thinking about moving out of New York and other big cities, and some have done so. These are responses more in keeping with the scale and drama of the episode that provoked them, but they may not make any more sense. David G. Myers of Hope College in Holland, Mich.

, calculated that terrorists would have to hijack 50 planes a year and kill everyone aboard before flying would be more dangerous than driving an equal distance. The steps we have taken to protect ourselves from terrorism (not counting the military effort to stop it at the source) seem either farcically trivial or farcically excessive. Is there a rational middle ground? Dealing rationally with the risks of terrorism is hard for several reasons. First, human beings are bad at assessing small risks of large catastrophes.

And Americans are especially bad at this because we are Americans, and catastrophes are not supposed to happen to us. Our legal culture, our political culture and our media culture all push us toward excessive caution by guaranteeing that any large disaster will produce an orgy of hindsight. Lawyers will sue, politicians will hold hearings, newspapers and newsmagazine's will publish overexcited revelations about secret memos that could be interpreted as having warned of this if held up to the light at a certain angle. Second, the actual risk of being a terror victim is not merely small-it is unknown and unknowable. Economists make a distinction between 'risk' and 'uncertainty.' Risk refers to hard mathematical odds. Uncertainty refers to situations in which the odds are anybody's guess Third, even knowing what is theoretically knowable is impossible for most of us.

Just attempting to list the fields of knowledge where expertise would be required strains my own ignorance: aeronautical engineering, Middle Eastern politics, nuclear physics, um, microbiology? Clinical psychology? Without a clue about most of these subjects, how can citizens think rationally about them? Walter Lippmann, in his famous 1922 book, Public Opinion, said the solution was to turn over most public-policy questions to boards of experts. Fourth, it's hard to be rational about the irrational. Who can guess intelligently what Osama bin Laden might want to try next? How can you discourage a suicide bomber who is looking forward to being dead after killing you? Irrationality holds a treasured place in game theory, the branch of economics dedicated to strategic questions of this sort. Game theory's great insight is that irrationality can be an asset. If you can convince the world that you " re nuts-and the surest way to do that is to be nuts-your behavior becomes impossible to predict or control. You become, in a way, invulnerable.

What all this adds up to is a strong suspicion that we are not doing too little about terrorism: we are probably doing too much. Our initial instincts are overly risk averse; the danger probably looms larger than it should. A crazed terrorist's next move is going to be a surprise: the burdens we impose on ourselves out of hindsight from the last episode are unlikely to be the ones hindsight will recommend after the next one. We can be skeptical about the warnings of terrorism 'experts.' They have a psychological or even financial interest in erring on the side of panic.

Before we avoid skyscrapers in case they are hit by hijacked airplanes, we should consider other risks and what we are doing to avoid them. About 4, 000 people die by accidental drowning every year. That's more than died on 9/11. Rationality cannot tell us precisely what it's worth to avoid an unknowable risk. But rationality can compare risks and gently suggest that you should not worry about one risk if you are happily oblivious to another. In short, a more rational approach to protecting ourselves from terrorism may not be doing more about it, or doing something different, but actually doing less.

We need the courage and good sense to bury our heads in the sand a bit.