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There is something about a first friend that is irreplaceable. No matter how disparately your lives travel, the first friend you ever had occupies a special place in your heart. I was lucky that Michael was considerate enough to be born four months before me, waiting next door, ready to join me in elaborate childhood games of hide-and-seek, multilevel couch forts and family camping trips in the Catskills.

Michael was quirky and inquisitive, equally adept at dismantling the innards of a telephone, figuring out how to sing “Hey Jude” backward, and testing the physics of fire escape ladders. We both became vegetarians at sleep-away camp — I because I thought it was cool, Michael because he literally couldn’t hurt a fly, protesting the flypaper strips that dangled from the ceilings and carrying spiders out of the cabin to set them free in a thicket of blackberry bushes.

When Michael killed himself during his sophomore year of college, it was a horrible shock. I’d known he’d been depressed, but we’d lost touch, so I hadn’t known the extent of it. But it was the fact the he’d shot himself in the face, in his childhood bedroom, while his parents and brother were watching TV downstairs that caused the most intense pain. How could someone who defended flies against the barbarity of flypaper find in himself the capacity for such violence?

As a physician, I know that suicide is the third leading cause of death for Michael’s cohort — 15- to 24-year-olds. Every year an estimated million people worldwide take their lives. It’s not just one million lives, but millions of families, friends and neighbors left with thorns in their hearts, black holes that may scab over but will never disappear.

Despite all the advances in depression treatment, mors voluntaria, or voluntary death, the Latin term for suicide, remains stubbornly persistent. I had always thought of suicide as what lay at the tarry depths of the funnel of mental illness. Then I came across an essay that offered a slightly different take.

In The Bellevue Literary Review, in an essay called “By My Own Hand,” Anita Darcel Taylor writes about her bipolar illness and depression:

I have no grand wish for death. I do not view suicide as a desire to end life or a dramatic way to go down in flames. Rather, it is a tool in my possession — the only one, really — that offers a permanent end to my pain. When I have lost enough of myself to this disease as to become unrecognizable even to me, I will stop. I will go no further. That, I tell myself, is my earned choice.

I have pondered these words many times. The clinician in me wants to insist that with the right tools — therapy, medications, support systems — most depressions can be treated. But the reality is that our tools are often no match for the fury.

Depression screening is now standard. Along with a blood pressure check, all my patients get a depression questionnaire. One question is: “Have you ever had thoughts that you would be better off dead?”

A surprising number of patients say they have, and I find myself in frequent existential conversations about life and death, hunting for pragmatic clues about actual risks for suicide. There are clinical guidelines for assessing risk, but it is an imperfect science.

Two weeks ago, I called one of my patients to reschedule an appointment. A family member answered and told me that my patient had been found dead in his apartment, most likely a suicide. This robust and healthy 54-year-old had screened “negative” for depression at every visit, despite having risk factors: being unemployed, living alone, caring for an ill relative.

I’m not ready to give up hope. I will continue to assiduously treat my patients’ depression, but I remain humbled by the fact that even with the best of medical science, we will be successful only in part. And of course there is — as Ms. Taylor points out — the voluntary aspect of mors voluntaria. For some people it might be a rationally used tool. For others, it is a tsunami without possibility of escape. It is precarious, from the outside, to judge.

I can never know how it was for Michael — whether it was a “rational” choice, or simply the relentless blackness of his illness. Despite the decades that have passed since his death, the sadness remains. The graphic nightmares of the gunshot, of his family scrambling to the bedroom, of the unimaginably horrific site that greeted them, have receded. But he comes to me from time to time, and I mourn the child that he was, and the adult that he never had the chance to become. As I watch my own children grow, I have a slip of insight into the exquisiteness of his parents’ pain — pain that surely travels with them always.

There is one photograph that comes to mind whenever I remember Michael. It was during a camping trip, and our green Coleman tent looms in the background. Our skinny 7-year-old arms flop over each other’s shoulders, and our mouths loll open, yodeling one of the many goofy songs in our repertory.

I want to yodel back into that scene, to those two children, to feel the insouciant, rapturous joy of that moment. If only I could tug out that feeling, wrap it around us like the oversize beach towels we loved, to somehow protect us from the future. I want to warn those children, to warn my own children who are now the same age, and who now go on those same camping trips and sing those same songs.

But I know that I can’t. I can only hope. Remember, and hope.