I think the NYT’s very illuminating look at the elusive quest for “metrics” in Afghanistan slightly misstates why it is that metrics matter to people:
Those “metrics” of success, demanded by Congress and eagerly awaited by the military, are seen as crucial if the president is to convince Capitol Hill and the country that his revamped strategy is working. Without concrete signs of progress, Mr. Obama may lack the political stock — especially among Democrats and his liberal base — to make the case for continuing the military effort or enlarging the American presence.
I think the issue is a bit less about “concrete signs of progress,” though those are always welcome, than they are about a desire to have some clarity about goals. If you flash back to the winter of 2001-2002, I think people were generally expecting the U.S. to topple the Taliban, kill or capture OBL, Zarqawi, and Mullah Omar, and then offer Afghanistan some kind of reconstruction help. But by failing to accomplish those core goals in a swift and decisive manner, the Bush administration wound up in a situation where the reconstruction shifted from a secondary objective to something more like a primary one, even though nobody would ever have said we should invade Afghanistan in order to undertake a lengthy and difficult nation-building operation.