...ideally shouldn't bank on one's enemy doing something really stupid. Such as, for example, trying to conquer Pakistan. Especially so when the Pakistani side of the border is where said enemy's supplies, reinforcements, and safe havens are.
Defeating the Taliban without the serious help of the Pakistanis would be extremely difficult. Thankfully, the Taliban seem to have done us a huge favor here. It won't be as easy fighting Nato in the West when the Pakistani army is coming simultaneously from the East.