It was in his self-neglect, rather than his hostility, that my father found common cause with the tens of millions of American patients who collectively hobble our health-care system.

For years, the United States’ high health-care costs and poor outcomes have provoked hand-wringing, and rightly so: Every other high-income country in the world spends less than America does as a share of GDP, and surpasses us in most key health outcomes.

Recriminations tend to focus on how Americans pay for health care, and on our hospitals and physicians. Surely if we could just import Singapore’s or Switzerland’s health-care system to our nation, the logic goes, we’d get those countries’ lower costs and better results. Surely, some might add, a program like Medicare for All would help by discouraging high-cost, ineffective treatments.

But lost in these discussions is, well, us. We ought to consider the possibility that if we exported Americans to those other countries, their systems might end up with our costs and outcomes. That although Americans (rightly, in my opinion) love the idea of Medicare for All, they would rebel at its reality. In other words, we need to ask: Could the problem with the American health-care system lie not only with the American system but with American patients?

One hint that patient behavior matters a lot is the tremendous variation in health outcomes among American states and even counties, despite the fact that they are all part of the same health-care system. A 2017 study published in JAMA Internal Medicine reported that 74 percent of the variation in life expectancy across counties is explained by health-related lifestyle factors such as inactivity and smoking, and by conditions associated with them, such as obesity and diabetes—which is to say, by patients themselves. If this is true across counties, it should be true across countries too. And indeed, many experts estimate that what providers do accounts for only 10 to 25 percent of life-expectancy improvements in a given country. What patients do seems to matter much more.

Somava Saha, a Boston-area physician who for more than 15 years practiced primary-care medicine and is now a vice president at the nonprofit Institute for Healthcare Improvement, told me that several unhealthy behaviors common among Americans (for example, a sedentary lifestyle) are partly rooted in cultural norms. Having worked on health-care projects around the world, she has concluded that a key motivator for healthy behavior is feeling integrated in a community where that behavior is commonplace. And sure enough, healthy community norms are particularly evident in certain places with strong outcome-to-cost ratios, like Sweden. Americans, with our relatively weak sense of community, are harder to influence. “We tend to see health as something that policy making or health-care systems ought to do for us,” she explained. To address the problem, Saha fostered health-boosting relationships within patient communities. She notes that patients in groups like these have been shown to have significantly better outcomes for an array of conditions, including diabetes and depression, than similar patients not in groups.