Rationalization is something we all do (often daily) when confronted with events that go against our plans and desires. The process is simple. We take a complex event, replete with unknowns, and put it into a framework where everything makes sense to us. The usual output of this process is "if only we had (or not) done this or that..." or "if we had taken this approach (substitute your pet theory here) things would have turned out grand."
We are now at the start of a long process of rationalization over the US defeat in Iraq. The most common of these rationalizations include: if only we had "...not disbanded the Baathist army," "...sent in more troops," or "...become better at nation-building." However, in each case the approach is one dimensional, since we tend to view ourselves as the only actors on the stage. The actions and reactions of the opposition are discounted and explained away as fluff and background noise (those pesky terrorists...).
A better, and more sane approach, is to embrace the concept that war is a conflict of minds. There are two sides. For every change in approach there will be counters mounted by the opposition. In the case of Iraq, that opposition was extremely difficult to beat since it was organized along the lines of open source warfare. This organizational structure gave it a level of innovation, resilience, and flexibility that made it a very effective opponent. Given this, the simplest explanation for the outcome in Iraq is that we were just beaten by a better opponent (the Israeli's seem to be getting this, why can't we?).
The real question we should be asking ourselves is whether or not our maximalist goals in Iraq could ever have been achieved given the capabilities of the opposition and the limited levels of commitment we were able to bring to to bear on the problem. I suspect the answer is no. The goals didn't match our capabilities and there weren't any simple tweaks to our strategy that would have changed the outcome. This was a difficult way to learn this lesson, but given our tendency towards rationalization, I doubt that it will be learned at all.God grant me the serenity to accept the things I cannot change, courage to change the things I can, and the wisdom to know the difference.