The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt.—Bertrand Russell
I read about the Dunning-Kruger effect on Nathan Branford’s blog and promptly followed his ink to the Wikipedia article about it. This explains so much about the world, like all the parents of youth fencers who complain at tournaments about the horrible referee whose bad calls rob their children of victory, when said bad official is a highly ranked and famously competent international referee.
I can remember indulging in such arrogance myself in other areas when I’ve known less than I thought I did.
At least the effect is remediable—you just have to learn more.