This explains a lot

From the WaPo:

Abrahams, who has a vast knowledge of improbable scientific literature, compares Gier's work to that of two Cornell scientists who showed that one attribute of extreme incompetence is "that the person so afflicted is incapable of knowing that he is incompetent." The study, titled "Unskilled and Unaware of It," demonstrated that people who scored, on average, at the 12th percentile in tests of humor, grammar and logic assessed themselves to be, on average, at the 62nd percentile. Incompetence at the extreme is a double-whammy, the authors declare: "Not only do these people reach erroneous conclusions and make unfortunate choices, but their incompetence robs them of the metacognitive ability to realize it." (Which explains Washington, in a nutshell.)

That said, what would you give to see where Dubya would actually test compared to where he thinks he would test? Take this factor along with the sheer quantity of sunshine blown up his ass on a daily basis, the yes men and the cockiness, and I bet you'd be looking at an absolutely unparalleled level of dissonance.