• Low-tech is very effective. Movie-plot threats -- terrorists with crop dusters, terrorists with biological agents, terrorists targeting our water supplies -- might be what people worry about, but a bunch of trained (we don't really know yet what sort of training they had, but it's clear that they had some) men with guns and grenades is all they needed.

• At the same time, the attacks were surprisingly ineffective. I can't find exact numbers, but it seems there were about 18 terrorists. The latest toll is 195 dead, 235 wounded. That's 11 dead, 13 wounded, per terrorist. As horrible as the reality is, that's much less than you might have thought if you imagined the movie in your head. Reality is different from the movies.

• Even so, terrorism is rare. If a bunch of men with guns and grenades is all they really need, then why isn't this sort of terrorism more common? Why not in the U.S., where it's easy to get hold of weapons? It's because terrorism is very, very rare.

• Specific countermeasures don't help against these attacks. None of the high-priced countermeasures that defend against specific tactics and specific targets made, or would have made, any difference: photo ID checks, confiscating liquids at airports, fingerprinting foreigners at the border, bag screening on public transportation, anything. Evenmetal detectors and threat warnings didn't do any good:

  "If I look at what we had, which all of us complained about, it could not have stopped what took place," he told CNN. "It's ironic that we did have such a warning, and we did have some measures."

  He said people were told to park away from the entrance and had to go through a metal detector. But he said the attackers came through a back entrance.

  "They knew what they were doing, and they did not go through the front. All of our arrangements are in the front," he said.

If there's any lesson in these attacks, it's not to focus too much on the specifics of the attacks. Of course, that's not the way we're programmed to think. We respond to stories and not analysis. I don't mean to be sympathetic; this tendency is human and these deaths are really tragic. But eighteen armed people intent on killing lots of innocents will be able to do just that, and last-line-of-defense countermeasures won't be able to stop them. Intelligence, investigation, and emergency response. We have to find and stop the terrorists before they attack, and deal with the aftermath of the attacks we don't stop. There really is no other way, and I hope that we don't let the tragedy lead us into unwise decisions about how to deal with terrorism.