Thomas Ricks nails it. ..

In dozens of official interviews compiled by the Army for its oral history archives, officers who had been involved in training and advising Iraqis bluntly criticized almost every aspect of the effort. Some officers thought that team members were often selected poorly. Others fretted that the soldiers who prepared them had never served in Iraq and lacked understanding of the tasks of training and advising. Many said they felt insufficiently supported by the Army while in Iraq, with intermittent shipments of supplies and interpreters who often did not seem to understand English.

[..]Some of the American officers even faulted their own lack of understanding of the task. "If I had to do it again, I know I'd do it completely different," reported Maj. Mike Sullivan, who advised an Iraqi army battalion in 2004. "I went there with the wrong attitude and I thought I understood Iraq and the history because I had seen PowerPoint slides, but I really didn't." Read on...