Twenty-five years ago, in December, 1989, Darkness Visible, William Styron’s account of his descent into the depths of clinical depression and back, appeared in Vanity Fair. The piece revealed in unsparing detail how Styron’s lifelong melancholy at once gave way to a seductive urge to end his own life. A few months later, he released the essay as a book, augmenting the article with a recollection of when the illness first took hold of him: in Paris, as he was about to accept the 1985 Prix mondial Cino Del Duca, the French literary award. By the author’s own acknowledgement, the response from readers was unprecedented. “This was just overwhelming. It was just by the thousands that the letters came in,” he told Charlie Rose. “I had not really realized that it was going to touch that kind of a nerve.”

Styron may have been startled by the outpouring of mail, but in many ways, it’s easy to understand. The academic research on mental illness at the time was relatively comprehensive, but no one to date had offered the kind of report that Styron gave to the public: a firsthand account of what it’s like to have the monstrous condition overtake you. He also exposed the inadequacy of the word itself, which is still used interchangeably to describe a case of the blues, rather than the tempestuous agony sufferers know too well.

Depression is notoriously hard to describe, but Styron managed to split the atom. “I’d feel the horror, like some poisonous fogbank, roll in upon my mind,” he wrote in one chapter. In another: “It is not an immediately identifiable pain, like that of a broken limb. It may be more accurate to say that despair… comes to resemble the diabolical discomfort of being imprisoned in a fiercely overheated room. And because no breeze stirs this cauldron... it is entirely natural that the victim begins to think ceaselessly of oblivion.”

As someone who has fought intermittently with the same illness since college, those sentences were cathartic, just as I suspect they were for the many readers who wrote to Styron disclosing unequivocally that he had saved their lives. As brutal as depression can be, one of the main ways a person can restrain it is through solidarity. You are not alone, Styron reminded his readers, and the fog will lift. Patience is paramount.

Given Styron’s monumental contribution to American literature, it could seem like a strange incongruity that this slim volume will likely end up as his most enduring work. But in many ways, Darkness Visible was the culmination of a lifetime spent grappling with the meaning of sorrow. In Sophie’s Choice, for instance, the black abyss is the legacy of the Holocaust. In Lie Down in Darkness, which explores the pride and guilt of the Deep South, the pain is shared among a grieving family. Both of these novels, it’s worth noting, involve a self-inflicted death.

In addition to the solace of recognition the book lent to its readers, it helped crack the stigma behind the condition. Sufferers today can turn to a wide body of personal writing on the subject, and a long line of public figures—from Mike Wallace to Brooke Shields—have spoken to the press about battling the illness. But Styron’s book was, in almost every way, a first, and for that reason, his memory is solidified not just as a great American writer but as a pioneering advocate for mental health.

It was a role he neither sought nor, by his daughter's account in her own memoir, wore lightly, responding to almost every letter he received. Like many people who have had a depressive episode in the past, Styron’s illness returned, after a 15-year respite. He was determined, however, that his own misfortune not tarnish the hope of the readers he had encouraged. Fearing he might take his own life (a fear, thankfully, never realized), Styron composed the following note:

I hope that readers of Darkness Visible—past, present and future—will not be discouraged by the manner of my dying… Everyone must keep up the struggle, for it is always likely that you will win the battle and nearly a certainty you will win the war. To all of you, sufferers and non-sufferers alike, I send my abiding love.

It is a testament to his stamina that, fending off the darkness yet again, he had the presence of mind to reassure his readers in the event of catastrophe. His career is a lesson in wringing dignity out of hardship.

At the end of Sophie’s Choice, Stingo, Styron’s alter-ego, makes his way onto the beach at Coney Island, ravaged by grief. He falls asleep in the sand and is greeted by terrifying visions, only to rise the next morning to the hopeful sounds of children and the brilliance of the early morning sky. The poem he writes for himself in this waking moment could also stand as an epitaph for Styron’s life—and the role he played in the lives of his readers:

'Neath cold sand I dreamed of death

But woke at dawn to see

In glory, the bright, the morning star.