The scariest thing Gen. McChrystal told Congress about Afghanistan.

At an otherwise uneventful hearing before the House Armed Services Committee this morning, Gen. Stanley McChrystal, the U.S. commander in Afghanistan, said something that should confirm and heighten most people's apprehensions about the war's escalation.

McChrystal noted that he has accumulated several years of command experience in that country since the war began. And yet, he confessed, "There is much in Afghanistan that I do not understand."

None of the legislators audibly gasped, or asked any questions about this remark, but they should have.

In most conventional wars, it doesn't much matter whether commanders or their subordinates have a deep feel for the psychology or culture of the people who live on or near the battlefield. However, in a counterinsurgency war, this sort of knowledge is essential.

As Gen. David Petraeus put it in his celebrated field manual on counterinsurgency (often abbreviated as COIN):

Successful conduct of COIN operations depends on thoroughly understanding the society and culture within which they are being conducted.

The manual then lists a few things that the soldiers and Marines who wage this sort of war "must understand"—including "Organization of key groups in the society"; "Relationships and tensions among groups"; "Ideologies and narratives that resonate with groups"; "Values of groups (including tribes), interests, and motivations"; "Means by which groups (including tribes) communicate"; and "The society's leadership system."

In other words, as the manual declares on Page 27, "Cultural knowledge is essential to waging a successful counterinsurgency."

McChrystal understands the central importance of this dimension. He and Petraeus (who is now U.S. commander of the entire region) have talked a great deal about exploiting divisions within the Taliban, splitting off its nonideological factions from the fundamentalists, and luring local or tribal leaders to join us in battling the insurgents.

But McChrystal's remark at this morning's hearing raises a vital question about our political and military leaders: How much do they really understand about what they know they must understand?