It is time to get real about Afghanistan. Withdrawal is not a serious option. The United States, NATO, the European Union and others have invested massively in stabilizing that country over the past eight years, and they should not abandon it because the Taliban is proving a tougher foe than anticipated. But there is still a large gap between the goals the Obama administration is outlining and the means available to achieve them. This gap is best closed not by sending in tens of thousands of more troops but, rather, by understanding the limits of what we can reasonably achieve in Afghanistan.