Exactly. No military power in the world will be able to defeat the Taliban. Eventually, the Afgan people will have to decide for themselves, NATO and the coalition can only do so much.
As much as that is true, the actual point of the statement is; there will be no gain by NATO/UN/Coalition forces/Nations by a victory in Afghanistan. The gain will be for the people of Afghanistan and their victory will be when they are able to maintain security without international intervention. This is really the only victory NATO, and by association, Canada, can strive for; an Afghanistan with a stable government (whatever form that may be), a solid security force, a fair justice system and strong economy... The only benefit coalition forces will gain from this is a stable region and the knowledge that an oppressed people have been given a chance at freedom.
Thus, the people who will be victorious at this end state will be the free people of Afghanistan.
As for the Taliban; the best way to defeat them in Afghanistan is to show the people how much better off they are without them. To accomplish this, we have to support the people, allow them to progress without oppression and protect them from those who would prevent this, until such a time as they have accomplished enough to want to protect themselves from those who would have them subdued and oppressed. This is what is going on now with the mission; Reconstruction, Education and Security. But it will take time... At least a generation or two. But, either way, it is the people of Afghanistan who will benefit from the labour of the coalition countries.
Personally, I believe we, as a free society, are morally obligated to help, in any way, any oppressed society at least gain the opportunity to attain freedom. But, that's just my point of view.