Over at Neurologica, Steven Novella explores the frequent disconnect between what people seem to think they know and what is actually so. Think of Jay Leno's old "Jaywalking" sketch in which he would ask random people on the street some fairly simple questions which some of them could not answer -- even though most folks, with a moment or two to think, probably should have come up with a correct answer.
Novella is commenting on the same kind of phenomena, and wondering about why it happens. He suggests a combination of several factors, such as media sensationalism, the tendency toward cognitive bias (we tend to believe an answer that fits what we think rather than one that does not) and the fitting of facts into narratives whether they actually fit or not.
I suspect he is probably on target -- at least, on the frequent occasions when I am mistaken, one of those factors seems to have played a considerable role. I may be a slow learner.
What piqued my curiosity was Novella's post title: "Why Is the Public So Wrong?" I'm afraid my own confirmation bias sprang to action even before I clicked the link and read, because I had an immediate answer: "Because it's made up of people."