In health policy circles (yes, those exist!), experts often refer to three aims for a modern health care system: to offer 1) universal access to 2) high quality medical care at 3) an affordable cost. Access, quality, and cost: a possibly unachievable set of goals, certainly in the U.S., where the quality of our care is decent (but uneven), while access to care and the high cost of our care compare dismally to almost every other developed country.

Suppose you were fixing the U.S. health care system and realized that increasing access to care would make it harder to control costs. Which of the three aims would you make your priority? I asked this question to a couple groups of people. One group came out strongly in favor of access, the other in favor of cost control. Can you guess who these two groups of people were?

I asked a group of undergrads at Duke to make the same guess. These undergraduates were taking my health policy course, and with that background were able to make some good guesses. Those prioritizing access: Some thought it might be a rural population with limited access to subspecialists. Others thought it might be a poor population with little access to health insurance. Those prioritizing costs: Some thought these might be fiscal conservatives, others thought they were large employers trying to hold down the cost of employee benefits. These were all really good guesses. Only one problem with them.

They are all wrong, very wrong. Instead, the two groups of people were the very same students who were taking my course. On the first day of class, you see, I had given them a writing assignment explaining why one of these three goals ought to be a priority for any reform of the U.S. health care system. But I did not allow them to choose which goal to defend. Instead, I required some students to defend the idea that costs ought to be the priority, and required other students to defend access to care. Several weeks later, at the end of a quiz, I asked the same students to indicate which of the three aims they would prioritize if they were in charge of the U.S. health system.

Their opinions in the fourth week of the semester were strongly influenced by the aims I had arbitrarily assigned them to defend in the first week.

Health care systems are complicated. When it comes to laptop computers, we can plausibly hope for low cost, high quality goods that meet most people’s needs. These three aims are even more achievable for a basic necessity like food. We can expect high quality, cheap food that everyone has access to. But health care markets are much more complicated than the markets for computers and food. In fact, health care markets often force us to make impossible choices.

Do we offer that new hepatitis C drug — at $90,000 per patient — to everyone who might benefit from it? Or would such a policy bankrupt us? No easy answer. It comes down to a difficult value judgment.

As it turns out, our value judgments are often psychologically frail. That’s what my first-week writing assignment had such a profound effect on student values. The writing assignment did not run in the face of a long held view. In fact, that first week of class was probably the first time most of these students had given a second of thought to the trade-off between health care access and cost. But soon after they wrote their essays, their values began to solidify. That is a scary phenomenon. Once people begin to take hold of a moral position, they are anchored to that view, raising questions about their ability to objectively weigh the moral trade-off as they learn more about the topic.

Rather than fear this moral anchoring, I have chosen to utilize it. First, by taking advantage of the phenomenon in my teaching. I think a good way to open people’s minds is to show them how easily their minds become closed.

Second, I keep this phenomenon in mind when espousing my own opinions. I am humbled by the knowledge that my own opinions are shaped by unconscious biases.

If more of us acknowledge the psychological forces that influence our values, maybe we would be less caustic in confronting people whose moral and political views differ from our own.

Peter Ubel is a physician and behavioral scientist who blogs at his self-titled site, Peter Ubel and can be reached on Twitter @PeterUbel.  He is the author of Critical Decisions: How You and Your Doctor Can Make the Right Medical Choices Together. This article originally appeared in Forbes.