In the exclusive world of classical music, it is not hard to find examples of a number of great performers who have shown a combination of very adult misbehavior and a very childish temperament. As in other fields, when the musician is of extraordinary talent, others tend to grant unusual leeway for personal recklessness, and a career can keep growing unabated. Milos Forman’s 1984 film “Amadeus” portrayed the life of Mozart as just such a story.

In the case of Ervin Nyiregyházi, a piano prodigy of dazzling skill born in Budapest in 1903, immaturity and outlandishness proved sadly consequential, leading to a rapid downward plunge. Niyregyházi evinced tremendous potential beginning at a young age, and was, at 13, the subject of the first scientific study of a child prodigy. The great composer Arnold Schoenberg once wrote of Nyiregyházi, in a note to Los Angeles Philharmonic conductor Otto Klemperer, “Such power of expression I have never heard before. … Technique: it is astonishing what and how he plays: one never has the sense that it is difficult, that it is technique at all, but rather that sheer force of will permits him to surmount all difficulties in realizing an idea. — You see I’m becoming almost poetic.”

Nyiregyházi was not only exceptionally skilled, but exceptionally dysfunctional. Like many outsized talents, he also demonstrated the cost of that talent in his wider life — in extremis. That he could not tie his own shoes or cut up his own food can be seen as a by-product of a smothering mother who pushed him to develop as a musician before all else. That he married 10 times, often in rapid succession, and never went long without mistresses and prostitutes into his 70s is harder to explain — but surely he would have had less opportunity to win women over without his brilliance at the keyboard. But that brilliance slipped from public view: By his mid-20s, he had burned enough bridges in America and Europe to sink any career into a deep trough.

Kevin Bazzana’s thorough and competent biography of Nyiregyházi, “Lost Genius” (Carroll & Graf, 400 pages, $28), charts what Mr. Bazzana calls “a picaresque tale, equally astonishing and sad, of the rise and fall and rise and fall of a genuine monstre sacré and musicien maudit.” Mr. Bazzana, who has previously impressed with “Wondrous Strange,” his highly regarded life of Glenn Gould, interprets the arc of Nyiregyházi ‘s lifetime not as an unfolding catastrophe, but as a tragedy of a more sweeping and philosophical kind — of a man whose uncompromising ideals as a composer and a performer rendered him, perhaps intentionally, “unfit psychologically” for conventional success. And indeed, the evidence of Nyiregyházi’s capacity for self-sabotage, which Mr. Bazzana has impressively marshaled, is so voluminous as to suggest some willfullness on Nyireghyazi’s part.

Still, such a portrayal falls short of accounting for his abnormally large collection of peccadilloes, and there is throughout this book the whiff of a writer who has fallen for his subject. Despite the inclusion of much unflattering detail, Mr. Bazzana is too soft on Nyireghyázi, and reading “Lost Genius,” which amounts to spending hours with an overgrown child, can be a maddening experience. Schoenberg and other luminaries praise Nyireghyázi’s accomplishments fulsomely — and Mr. Bazzana himself calls a few of his recordings “among the most astonishing piano performances ever recorded” — but this has the effect of making us ardently long for Nyireghyázi the petty man to get out of the way of Nyireghyázi the magnificent pianist.

With his subject, Mr. Bazzana clearly faced a classic biographer’s problem: Given the inherent limits of available documentation and memories, do you place a great deal of weight on what you have, constructing elaborate explanations of behavior and personality on a shaky foundation? Or do you regard, say, 20 truly revealing journal entries and letters as nothing more than an obviously incomplete record of a man’s interior life at a single moment? Mr. Bazzana takes the responsible approach and allows the facts to speak without bending them to a psychological explanation. That’s to his credit, but the unfortunate result for a reader hungry for meaty material is something that resembles a bildungsroman with a main character who lacks a vital, beating heart. The most engrossing aspects of the book are not the intimate details of Nyireghyázi’s marriages and personal life but the careful and erudite descriptions of Nyireghyázi’s playing — something of a feat in an account of a pianist long dead. For example:

His command of the sustaining pedal contributed much to his tone and phrasing, but he pedalled for other reasons, too: to ‘develop’ a sonority after the strings had been struck (he could make the piano’s tone seem to swell rather than decay), to create walls of sound in emotionally charged passages. … ‘Harmonically it may not be distinct,’ he said of one such passage, ‘but emotionally it is right!’

Nyireghyázi experienced a career revival in his 70s, after decades in which he could be found playing in brothels. The fad didn’t last. Notwithstanding Mr. Bazzana’s conclusions, the story of this Hungarian musician seems to me a frustrating but also moving tale of a grand failure brought on by social ineptitude and bad behavior.

Mr. Hughes has written for the London Review of Books, the New York Review of Books, and the New York Times, among other publications.