Iraq never "succeeded". The US made a hasty exit from there and the Taliban took over. Just like they're doing in Afghanistan.

The Taliban has been able to "hide out" in neighboring Pakistan. A similar problem occurred in Iraq with regard to ISIS...but ALL of the national governments in the region were actively (and desperately) trying to quash ISIS. Eventually, ISIS was eradicated in Iraq and neighboring regions. Pakistan does not view the Taliban as a significant national threat (and rightly so), and so is not making a desperate and expensive effort to quash the Taliban in Pakistan. Thus, over the years the Taliban has been hanging out in western Pakistan and in fact growing in strength there. *IF* the Taliban had been restricted to Afghani territory, they could have been quashed during the prolonged confrontation. They would have grown weaker and weaker and would not have survived the "war of attrition". As it is, they are able to survive the prolonged engagement, returning (with attempts to conquer Afghanistan) every few years with restored strength. In such a war WE (the U.S.) cannot win because we as a nation do not have the "political will" to continue the war indefinitely, nor the political will to "force" Pakistan to eradicate the Taliban on their side of the border, nor the political will to cross that border ourselves (invading Pakistan) to eradicate the Taliban there. Perhaps if the Taliban retakes Afghanistan we will muster such a strong "political will"...or perhaps it will take another 9-11. We'll see.