You guys might want to check out the link for "Unskilled and Unaware of It: How Difficulties in Recognizing One's Own Incompetence Lead to Inflated Self-Assessments" in that wikipedia article. The author, Kruger, has a great sense of humor.
And, "On the Psychology of Military Incompetence", by Dr Norman F. Dixon is worth a read.
I believe ignorance is common. I also believe our experience is defined by what we can quantify. Many things can only be quantified by the willingness of others to believe them. If someone is in-tune with the majority thinking, they are backed by a world of reinforcement. So they are "cocksure". Those with ideas that aren't, experience more doubt than the average individual.
Not sure this is solely confined to intelligence though.
This is only the first layer of what could be called the ego-reality relation. There is a meta-effect to this effect where people who believe they are more complicated in thought factor doubt into their persona because it reinforces a false sense of info absorption as well as give themselves sway over those who wish to encourage the implications of this primary effect in discussion.
The entire ego-reality relation is a manner by which a human nature compensates for actual reality of have and have nots. The false sense of info absorption leads to unnecessary hesitation and inefficiency, and the sway leads to ego-enabling which only serves to distance the person from actual reality.
Actual reality plays no such ego games and there are no effects such as this apart from what is introduced into reality by ego (and thus only real in the same sense that counterfeit money is printed on real paper). In actual reality, intelligence mirrors reality and because that is what the pure definition of intelligence should be, it begets knowledge of actual cause and effect, leading to proficiency and eventually confidence.
In other words, what this effect attempts to quantify is that the ego is ignorant, and it is. However, the conclusions are false, because doubt it a construct of the ego as well. In fact, the mere implication that there is a dichotomy of intelligence involved is delusive. There is reality, and there is the ego, which always involves a degree of un-reality. No dichotomy.
Yes, I knew about this, and it causes me great insecurity.
The moment I think I'm good at something, I think of this.
Then I think "well, if you doubt yourself by thinking of that, then is that not evidence you are one of the competent and not one of the incompetent?".
But then I reason that if I actually bought into that, I'd have self-confidence which would once again leave me vulnerable to becoming a self-assured dolt, or that I may in fact be one already.
So then I decide that I can't know if I'm competent or not just by judging myself, and I figure that it's safer for me to just keep doubting myself, since that allows more for the possiiblity that I actually am competent.
This cycle plays out in my head on a regular basis.