We may not slaughter animals anymore to ward off a plague, but we think buying health insurance will keep us from getting sick. Our brains may understand meteorology, but in our guts we still think that not carrying an umbrella will make it rain, a belief that was demonstrated in experiments by Jane Risen of the University of Chicago and Thomas Gilovich of Cornell.
I think this could be really important. In general, I am not a fan of behavioral economics, but I do think that human beings have a very hard time dealing with uncertainty and probability. For example, doctors do not understand Bayes' theorem, as Ian Ayres' Supercrunchers documents.
I remember John Kerry's ads saying "I'll give you health care." He meant health insurance, but people equate insurance, which ought to be financial protection, with care. People are buying health insurance to protect against the fear of not being treated*, rather than buying it to protect against the risk of really large medical bills.
(*Some of that fear is rational, I know. Try walking into a hospital with thousands of dollars in cash but no insurance card.)