Donald J. Trump has regularly boasted about “The Art of the Deal,” his best-selling autobiography, as a business bible that demonstrates the sharp negotiating prowess he would bring to the presidency. The book, released in 1987, details his rise to the top of New York’s real estate world; it helped spawn his career as a reality television star and cemented his image as a winner with a golden touch.

But Tony Schwartz, the book’s ghostwriter, who spent 18 months in the 1980s interviewing and shadowing Mr. Trump, says that it is really a work of fiction.

In an interview with The New Yorker magazine for its July 25 issue, Mr. Schwartz explained publicly, and for the first time, what he learned from living in Mr. Trump’s world. Here are some highlights.

The Art of Regret

Mr. Schwartz, a former magazine writer who said he worked on the book because he needed the money, told the writer Jane Mayer that he painted Mr. Trump in the most positive light that he could, thinking that a sympathetic character would be better for the book’s sales than a story about a cruel tycoon. If he could do it over again, however, Mr. Schwartz said the book would be titled “The Sociopath.”