At a recent town hall meeting, a man stood up and told Representative Bob Inglis to “keep your government hands off my Medicare.” The congressman, a Republican from South Carolina, tried to explain that Medicare is already a government program  but the voter, Mr. Inglis said, “wasn’t having any of it.”

It’s a funny story  but it illustrates the extent to which health reform must climb a wall of misinformation. It’s not just that many Americans don’t understand what President Obama is proposing; many people don’t understand the way American health care works right now. They don’t understand, in particular, that getting the government involved in health care wouldn’t be a radical step: the government is already deeply involved, even in private insurance.

And that government involvement is the only reason our system works at all.

The key thing you need to know about health care is that it depends crucially on insurance. You don’t know when or whether you’ll need treatment  but if you do, treatment can be extremely expensive, well beyond what most people can pay out of pocket. Triple coronary bypasses, not routine doctor’s visits, are where the real money is, so insurance is essential.

Yet private markets for health insurance, left to their own devices, work very badly: insurers deny as many claims as possible, and they also try to avoid covering people who are likely to need care. Horror stories are legion: the insurance company that refused to pay for urgently needed cancer surgery because of questions about the patient’s acne treatment; the healthy young woman denied coverage because she briefly saw a psychologist after breaking up with her boyfriend.