"Ignorance more frequently begets confidence than does knowledge."
We've all heard of the Peter Principle, the idea that people tend to be promoted to the level of their incompetence. Few are aware of an even more dangerous phenomenon, however--the fact that the least competent among us are the least able to see their incompetence, otherwise known as the "Dunning-Kruger Effect."
Described by psychologists David Dunning and Justin Kruger, the Dunning-Kruger Effect (DKE) is the phenomenon where the people who are least competent in an area are the least able to judge their competence and the most likely to be overconfident in their expertise. They will also be least likely to be able to recognize competence in others, so they tend to ignore or dismiss experts because they don't actually recognize their expertise.
One of the best examples of the DKE is the Stephen Colbert show, in which he plays an ignorant host with little knowledge but very confident opinions about everything. Other blatant examples include: