The Dunning-Kruger Effect

A cognitive bias in which "people reach erroneous conclusions and make unfortunate choices but their incompetence robs them of the metacognitive ability to realize it."

The unskilled therefore suffer from illusory superiority, rating their own ability as above average, much higher than actuality; by contrast the highly skilled underrate their abilities, suffering from illusory inferiority. This leads to a perverse result where less competent people will rate their own ability higher than relatively more competent people. It also explains why actual competence may weaken self-confidence because competent individuals falsely assume that others have an equivalent understanding. "Thus, the miscalibration of the incompetent stems from an error about the self, whereas the miscalibration of the highly competent stems from an error about others."

Ever notice that the more you know about something the more cautious you are about making sweeping generalizations? This may come across as a more tentative grasp of the subject than someone more self-assured. The more we know the more we seem to realize what we don't know. This is why, I believe, the most persuasive politicians and news channels can be the most incompetent perspectives on a situation but appear the most authoritative. It's human nature :-)

List of Cognitive Biases