Here's the obligatory reference for this discussion. Though since I last read it, I heard that the authors made some mistakes with their statistics so I guess one may choose not to believe it:
Journal of Personality and Social Psychology
1999, Vol. 77, No. 6. ] 121-1134
Copyright 1999 by the American Psychological Association, Inc.
0022-3514/99/S3.00
Unskilled and Unaware of It: How Difficulties in Recognizing One's Own
Incompetence Lead to Inflated Self-Assessments
Justin Kruger and David Dunning
Cornell Univer
http://blog.bruceabernethy.com/mirror/unskilled.pdf