(Fortune) -- Twenty-five years ago, when he was asked to assemble a list of the "Ten Books That Shaped the American Character," critic Jonathan Yardley summoned the works of the great ones: Thoreau and Whitman, Twain and Hemingway, Thorstein Veblen and W.E.B. Du Bois. And standing next to them in this pantheon of the nation's literary giants, he also placed the man who once told America to read his work "with a crayon, pencil, pen, magic marker, or highlighter in your hand. When you come across a suggestion that you feel you can use, draw a line beside it."
Since then, more than 30 million people worldwide have been embellishing, bedecking, and otherwise disfiguring their copies of How to Win Friends and Influence People, by Dale Carnegie. Upon its release in February, an iPhone app loaded with videos, charts, and homilies immediately became the top-selling paid business app in the iTunes store (it just landed on the iPad as well), and a new edition of the book -- only the second since its original publication -- may be arriving in stores next year. Not that Dale's heirs need the money; HTWF is already the most successful business advice book in the history of the solar system. Originally published in 1936, it has been translated into 47 languages, including Hindi, Nepalese, and Telugu. Last year alone, the very fortunate Simon & Schuster, which has controlled the rights to HTWF since its birth, sold 300,000 copies -- hardcover, paperback, and audio -- just in the U.S. By comparison, Malcolm Gladwell is a parvenu.
Like all great successes, HTWF has inspired backlash too, including at least four books and one movie all titled How to Lose Friends and Alienate People. But the book is also the foundation stone of a self-improvement empire, now called Dale Carnegie Training, that has franchises in 80 countries and claims 8 million graduates, including Warren Buffett, Frank Perdue, Lee Iacocca, and at least two generations of Dallas Cowboys cheerleaders.
Dale Carnegie clearly knew a hell of a lot about business.
Except he didn't. Born in 1888, the phenomenally successful dispenser of business advice had virtually no business background. Raised on a pig farm in Missouri, he first stumbled trying to sell correspondence courses, and then for a while he peddled bacon and lard in western South Dakota.
He was reasonably successful at that, but gave it up to move east in his early twenties, hoping to make it as an actor. That didn't work, and neither did selling trucks or writing western novels. What did work was the class in effective public speaking that he began to teach to a handful of students at a Harlem YMCA in 1912 -- a class that would form the basis of his philosophy, his methodology, and his mighty self-improvement empire. One of the smartest decisions he made was changing his name in 1919 from Carnagey to Carnegie, at a time when "Carnegie" carried the same aura that "Gates" does today.
But the real key to his eventual triumph, and probably the reason HTWF still holds up today, was the innate connection he sensed between public speaking and professional success. Warren Buffett says he was motivated to take the Carnegie course as a 20-year-old, when the prospect of public speaking would cause him to vomit. Iacocca tells a similar story: "For the first few years of my life I was an introvert, a shrinking violet," he wrote. Post-Carnegie, he was on the path to becoming the unshrunken, Carnegie-ized Iacocca who was the most visible American businessman of the 1980s.
To this day, Buffett keeps his Dale Carnegie diploma close at hand in his office. "It changed my life," he has said.
Effective public speaking, still the core of the Carnegie philosophy, is a matter of self-confidence -- which, tethered to the 30 principles that are the backbone of HTWF, can presumably produce a very effective person. It's as if Carnegie were saying, "If you can get up in front of a crowd and hold its attention, you can accomplish almost anything."
Those 30 principles are somewhat less complicated than particle physics. Or long division. The essential one is No. 3: "Arouse in the other person an eager want." Others could have come from a stern but kindly grade school teacher: "The only way to get the best of an argument is to avoid it" or "Let the other person do a great deal of the talking."
Before you scoff at those chestnuts, bear in mind that the best advice is usually obvious, and rarely followed (don't have that second martini, wear a sweater or you'll catch cold). One would like to think that what the Carnegie method advocated in 1937 still applies in 2010: The traits that make all human interaction possible -- manners, decency, generosity of spirit -- matter as much in business as they do in private life.
Carnegie himself once told a skeptical audience, "I've never claimed to have a new idea. Of course I deal with the obvious. I present, reiterate, and glorify the obvious -- because the obvious is what people need to be told." Even more obvious: People are willing to listen.