It's all about the Dunning-Kruger Effect - which is basically that incompetent people are too ignorant to know they are incompetent.
"When people are incompetent in the strategies they adopt to achieve success and satisfaction, they suffer a dual burden: Not only do they reach erroneous conclusions and make unfortunate choices, but their incompetence robs them of the ability to realize it. Instead, they are left with the erroneous impression they are doing just fine."
"When you’re incompetent, the skills you need to produce a right answer are exactly the skills you need to recognize what a right answer is."
"Many tasks in life contain uncertainties that are known — so-called known unknowns. These are potential problems for any venture, but they at least are problems that people can be vigilant about, prepare for, take insurance on, and often head off at the pass. Unknown unknown risks, on the other hand, are problems that people do not know they are vulnerable to."
"Unknown unknown solutions haunt the mediocre without their knowledge. The average detective does not realize the clues he or she neglects. The mediocre doctor is not aware of the diagnostic possibilities or treatments never considered. The run-of-the-mill lawyer fails to recognize the winning legal argument that is out there. People fail to reach their potential as professionals, lovers, parents and people simply because they are not aware of the possible."
"Ignorance is infinite but knowledge is finite."
"Some people have barriers to understanding an explanation of something, or a solution to a problem due to bias, and of these there are two general types. Some people have a religious or political belief system that would be undermined by any information that posed a contradiction to it and therefore certain possibilities and explanations are unacceptable -- ideas that other people find perfectly reasonable and sensible are ignored or treated as utter nonsense -- no argument is persuasive, so these people are immune to new information and knowledge.
There are also people with egos and self-esteem so outsized as to prevent them from hearing or accepting any challenge to their will or desires; psychologically they cannot afford to be wrong, or their sense of themselves would crumble. Frequently, their explanation for any error in judgement is that it is somebody else's fault; the test was unfair, the deck was stacked, they have enemies.
The real danger is when the two things are combined -- an intransigent belief system and an outsized ego. Someone like Sarah Palin comes to mind. She is stunningly ignorant and so filled with hubris and a sense of being "called by God" that it prevents her from realizing just how ignorant she is, so every challenge to her thinking is dismissed and derided."
"He who knows and knows he knows is a wise man, seek him;
he who knows and and knows not he knows is asleep, wake him;
he who knows not and knows he knows not is a child, teach him;
he who knows not and knows not he knows not is a fool - shun him!"
Kurt Vonnegut, describing of one of his characters, wrote, "He was too stupid to realize that there was such a thing as being smart."
"Ignorance can be cured, but stupid is forever."
Mark Twain: "It's not the things I don't know that worry me. It's the things I know for sure that just ain't so."
"Show me a thoroughly satisfied man and I will show you a failure." -- Thomas Edison
And a quote from one of my LJ friends: Humans are the only creatures smart enough to realize how stupid they are.