The truth is: Our generals can't quite tell us what our "mission" in Afghanistan is: First, there is no way we can defeat the Taliban, since they enjoy too much popular support in the rural areas, which is the majority of that country. Even though we've been there for nine years, the Taliban are still controlling that country. After nine years, the Taliban, not our army control the environment in our combat areas, and so far, we have only completely run the Taliban out of 3% of Afghanistan. During World War II, it took us only eleven months after D-day to entirely defeat the Nazis across all of Europe. In addition, our troops and their commanders are still trying to learn the language, the culture, and the customs of Afghanistan. After they have killed numerous civilians, through recklessness or for sport, our troops are simply not trusted by most of the citizens of Afghanistan.
In addition, the Afghan government we installed is corrupt beyond belief, no wonder their citizens don't trust them. "President" Karzai is on anti-depressants, and our advisors (my job in Vietnam) tell us he is erratic and "loopy" much of the time. (Don't forget that he once ran a coffee shop in New York, hardly a good background for running a country, especially one embroiled in a serious war.)
Before I became an advisory team leader in Vietnam, I had at least a reasonably solid military background!