Why Is The Truth So Often The Reverse Of Conventional Wisdom?

Lunch with an Afghan friend had me asking this question a few weeks back:

common wisdom is that Afghanistan is the Just War that is going well and Iraq is the disaster that's been mishandled from the get-go. I wonder if history will vindicate that view.

Michael Yon, citing this report on two attacks on a base in Afghanistan (which he predicted in Fall of 2006), writes to Instapundit:

We are winning in Iraq. Make no mistake about that. But we are losing in Afghanistan.