A study done by the psychology department at Cornell and published in the December issue of the "Journal of Personality and Social Psychology"
finds at least two reasons for the blissful ignorant:
Ignorant people tend to be confident of their abilities: more confident than people who are skilled and do things well.
Also, the ability to recognize competence is probably very closely related to be ability to be confident.
For more information:
http://www.zenspider.com/RWD/Thoughts/Inept.html
Obviously, having read this reasearch, all of us competent people are mentally reviewing our areas of incompetence.