NATO and the U.S. realized that the number of troops they deployed to Afghanistan were not enough to fend off an insurgency. They also knew that the European members of NATO would never be able to muster up enough troops to fend off an insurgency - which is the problem today (always has been).

After Tora Bora, the battle that ended the U.S. proxy war in Afghanistan, the U.S. realized that it was now in the business of economic and political reform, nation building, reconstruction and development. People like Bush, Cheney and Rumsfeld weren't into that. They were into war instead. So while they planned and executed the Iraq war, they left us European, Australian, New Zealand and Canadian suckers to hold the bag in Afghanistan.

ISAF troops first hit the ground in Afghanistan on December 20, 2001. The Pentagon appointed Hamid Karzai puppet regime arrived on December 25, 2001 (Chritmas Day). The original mission was to be the bodyguard of Karzai and his ministers by making sure Kabul was secure. Under U.S. pressure, the war escalated by expanding the mission to:

1. Provide security for Northern Afghan cities.

2. Provide security for Northern Afghanistan.

3. Provide security for Southern Afghan cities.

4. Provide security for Southern (all of) Afghanistan.

Aside from adding additional political goals to the war, which by now have all been pared back down the the original reasonable security with making sure that Afghansitan (hopefully) doesn't become a safe haven for terrorism.

At NO POINT has either the U.S. or NATO ever said "We are going to win the war" or promulgated a clear victory strategy.

The reason why they want stability in Afghanistan is so a Trans Afghan Pipeline (TAP) can be constructed. So long as they can achieve that, good enough, as far as they are concerned. Winning the war is not essential. If the war continues perpetually, so be it. It will help with unemployment and stimulate the arms industries.

How much of a genius does the U.S., NATO and Europe need to be to realize that we could never win the war in Afghanistan?

It's not like the British didn't have any experience in Afghanistan. See the year 1839. I mean, it's not like there wasn't a Soviet Afghan War. It's not like there wasn't the Vietnam War. It's not like there weren't neo colonial wars of independence that occurred throughout the 1950s, '60s and '70s. 

It's like Hans Christian Anderson's "The Emperor's New Clothes". All the leaders of the countries involved in the Afghan war see all the nakedness and ugliness of what is going on. None have the courage and virtue of the child in the story to admit that we are wrong and to end the war and bring our troops home now!