Joe Klein writes:

A few weeks ago, a well-known U.S. military expert gave a wise speech about the near impossibility of making a counterinsurgency (COIN) strategy work in Afghanistan. He gave two examples. The first was digging a well: "How could you do anything wrong by digging a well to give people clean water?" Well, you could create new enemies by where you dug the well and who controlled it. You could lose a village by trying to help it. And then there was the matter of what he called COIN mathematics. If there are 10 Taliban and you kill two, how many do you have left? Eight, perhaps. Or there might be two, because six of the remaining eight decide it's just not worth fighting anymore. Or you might have 20 because the brothers and cousins of the two dead fighters decide to take vengeance. "When I am asked what approach we should take in Afghanistan," General Stanley McChrystal concluded, "I say humility."