Which is a huge skillset in college, and not nearly as important in the NFL. He hasn't stayed at any place really long enough to demonstrate his ability to develop a system. And his appeal has largely been his ability to be larger than life to the people he's recruiting/coaching.
In the NFL, he's going to be coaching guys that are as talented (or at least believe they are as talented) as he ever was, which is a very different dynamic than anything he's had to deal with. He is anything but a sure thing.
That said, I want him to be the Cowboys coach, and I would even like to see him be successful. That would be a fun story, and since I don't really have an NFL team that I ride and die for, I am all about the good stories.