The following was delivered as the commencement address at U.C.L.A. Medical School on Friday, June 1st.

I want to start with a story. One night, on my surgery rotation, during my third year of medical school, I followed my chief resident into the trauma bay in the emergency department. We’d been summoned to see a prisoner who’d swallowed half a razor blade and slashed his left wrist with the corner of the crimp on a toothpaste tube. He was about thirty, built like a boxer, with a tattooed neck, hands shackled to the gurney, and gauze around his left wrist showing bright crimson seeping through.

The first thing out of his mouth was a creepy comment about the chief resident, an Asian-American woman. I won’t say what he said. Just know he managed in only a few words to be racist, sexist, and utterly menacing to her. She turned on her heels, handed me the clipboard, and said, “He’s all yours.”

I looked at the two policemen with him to see what they were going to do. I don’t know what I expected. That they’d yell at him? Beat him? But they only looked at me impassively, maybe slightly amused. He was all mine.

So what now?

Graduates, wherever you go from here, and whatever you do, you will be tested. And the test will be about your ability to hold onto your principles. The foundational principle of medicine, going back centuries, is that all lives are of equal worth.

This is a radical idea, one ultimately inscribed in our nation’s founding documents: we are all created equal and should be respected as such. I do not think it a mere coincidence that among the fifty-six founding fathers who signed the declaration of our independence was a physician, Dr. Benjamin Rush. He was a committed revolutionary and abolitionist precisely because of his belief in the principle.

We in medicine do not always live up to that principle. History has been about the struggle to close the gap between the aspiration and the reality. But when that gap is exposed—when it turns out that some people get worse or no treatment because of their lack of money, lack of connections, background, darker skin pigment, or additional X chromosome—we are at least ashamed about it. We believe a C.E.O. and a cabbie with the same heart disease deserve the same chance at survival.

Hospitals are one of the very few places left where you encounter the whole span of society. Walking the halls, you begin to understand that the average American is someone who has a high-school education and thirty thousand dollars a year in per-capita earnings, out of which thirty per cent goes to taxes and another thirty per cent to housing and health-care costs. (These Americans are also told, by the way, that people like them, the majority of the population, have no future in a knowledge economy, because, hey, what can anyone do about it, anyway?) Working in health care, you also know, more than most, that we incarcerate more people than any other economically developed country; that thirty per cent of adults carry a criminal arrest record; that seven million people are currently incarcerated, on parole, or on probation; and that a massive and troubling proportion of all of them are mentally ill or black.

Most people don’t have this broad vantage. We all occupy our own bubbles. Trust in others, even our neighbors, is at an historic low. Much of society has become like an airplane boarding line, with different rights and privileges for zones one to ninety-seven, depending on your wealth, frequent-flier miles, credit rating, and S.A.T. scores; and many of those in line think—though no one likes to admit it—that they deserve what they have more than the others behind them. Then the boarding agent catches some people from zone eighty-four jumping ahead of the people in zone fifty-seven, and all hell breaks loose.

Insisting that people are equally worthy of respect is an especially challenging idea today. In medicine, you see people who are troublesome in every way: the complainer, the person with the unfriendly tone, the unwitting bigot, the guy who, as they say, makes “poor life choices.” People can be untrustworthy, even scary. When they’re an actual threat—as the inmate was for my chief resident—you have to walk away. But you will also see lots of people whom you might have written off prove generous, caring, resourceful, brilliant. You don’t have to like or trust everyone to believe their lives are worth preserving.

We’ve divided the world into us versus them—an ever-shrinking population of good people against bad ones. But it’s not a dichotomy. People can be doers of good in many circumstances. And they can be doers of bad in others. It’s true of all of us. We are not sufficiently described by the best thing we have ever done, nor are we sufficiently described by the worst thing we have ever done. We are all of it.

Regarding people as having lives of equal worth means recognizing each as having a common core of humanity. Without being open to their humanity, it is impossible to provide good care to people—to insure, for instance, that you’ve given them enough anesthetic before doing a procedure. To see their humanity, you must put yourself in their shoes. That requires a willingness to ask people what it’s like in those shoes. It requires curiosity about others and the world beyond your boarding zone.

We are in a dangerous moment because every kind of curiosity is under attack—scientific curiosity, journalistic curiosity, artistic curiosity, cultural curiosity. This is what happens when the abiding emotions have become anger and fear. Underneath that anger and fear are often legitimate feelings of being ignored and unheard—a sense, for many, that others don’t care what it’s like in their shoes. So why offer curiosity to anyone else?

Once we lose the desire to understand—to be surprised, to listen and bear witness—we lose our humanity. Among the most important capacities that you take with you today is your curiosity. You must guard it, for curiosity is the beginning of empathy. When others say that someone is evil or crazy, or even a hero or an angel, they are usually trying to shut off curiosity. Don’t let them. We are all capable of heroic and of evil things. No one and nothing that you encounter in your life and career will be simply heroic or evil. Virtue is a capacity. It can always be lost or gained. That potential is why all of our lives are of equal worth.

In medicine, you are asked to open yourself to others’ lives and perspectives—to people as well as to circumstances you do not and perhaps will not understand. This is part of what I love most about this profession. It aims to sustain bedrock values that matter across all of society.

But the work of preserving those values is hard. When I began my story, I made a point of not telling you the inmate’s crime, although one of the policemen told me. I wasn’t sure whether it’d change how open you’d be to putting yourself in my shoes as I wrestled with what to do.