In truth, the only people who can profit from such a warning are the officials who issue it. If something does happen, they are covered: They warned us, they told us in advance, they won’t be criticized or forced to resign. And if nothing happens, then we’ll all forget about it anyway.

Except that we don’t forget about it. Over time, these kinds of enigmatic warnings do al-Qaeda’s work for it, scaring people without cause. Without so much as lifting a finger, Osama bin Laden disrupts our sense of security and well-being. At the same time, such warnings put the U.S. government in the position of the boy who cried wolf. The more often general warnings are issued, the less likely we are to heed them. We are perhaps unsettled or unnerved, but we don’t know what to do. So we do nothing — and wish that we’d been told nothing as well.