(FORTUNE Magazine) – An excellent way to embarrass your friends this fall is to ask them the name of the current No. 1 best-selling business book. It isn't a trick question; the book has been No. 1 on virtually every list--New York Times, Wall Street Journal, Business Week, USA Today--virtually every week for the past three months. Still, the odds are strong that your victims will have no idea what this megaseller might be. So you tell them. Then brace yourself, because they're likely to ask you a question: How could any book with such a stupid title become so hot?

Who Moved My Cheese?, by Spencer Johnson, is what publishers call a phenomenon, a book that with little or no conventional help somehow pulls itself from the vast, seething pit of loser titles and starts selling big. Until this moment you have not read a single article about Who Moved My Cheese? in any national magazine. You have not seen a single advertisement for it in any major national publication. You have not seen or heard the author interviewed about it because when he set out on his author's tour last fall, he got no bookings. Zero.

Yet the book is huge. How huge? Understand that a book can hit No. 1 on a weekly bestseller list but never sell more than 50,000 or 60,000 copies total. Who Moved My Cheese? is somewhere north of 500,000 copies so far, with sales holding steady week after week.

Most authors will only dream of achieving such success. But if you ask Johnson how his book is selling, he says, "The numbers are still relatively small." That's because he is--the name sounds familiar, right?--co-author (with Ken Blanchard) of The One Minute Manager, the 1981 parable that remains one of the best-selling books of any kind, with 11 million copies in print. Johnson followed that with a string of sequels--The One Minute Mother, The One Minute Father, The One Minute Teacher, The One Minute Sales Person--seven bestsellers in all, before this one.

And what is this one, with its ridiculous title? Like most of Johnson's books, it's a little story, in this case an allegory about change. It concerns two mice and two small humans who live in a maze where they find cheese, and how they respond when one day their cheese isn't where it used to be. The book is short. At 94 pages, it is padded, with some pages holding only six or eight words; you can read it in 45 minutes if you take it slow.

If you are determined to despise the book, Johnson makes it easy for you. With each copy he includes a pocket-sized card summarizing the book's main precepts, each followed by a brief amplification. For example:

--CHANGE HAPPENS They keep moving the cheese.

--ANTICIPATE CHANGE Get ready for the cheese to move.

--MONITOR CHANGE Smell the cheese often so that you know when it is getting old.

If this sort of thing makes you want to scream, you've got company. A minority of readers hate the book--"hate it with a capital 'H,'" as Johnson acknowledges. They've weighed in at Amazon.com, calling it "worthless drivel" and "simplistic pap." "If you need any more proof we are doomed as a society, this is it," concludes a California reader.

But what's most striking about the reader response to Who Moved My Cheese? is how many people feel it speaks to them in some deep way. The majority of reader reviews at Amazon.com are raves. More impressive is that many of the book's biggest fans are hardheaded business people; they are reading it, recommending it, and using it at their companies.

Procter & Gamble CEO Durk Jager, as tough a customer as you'll ever meet, recommended the book in a companywide e-mail. At least one manager at General Electric, bastion of cold-eyed assessments and results above all, is using it: Chris Oefinger of GE Mortgage in Dallas puts on education programs built around the book. Shortly before Lew Platt retired as Hewlett-Packard's CEO, he talked about the book in a major speech, declaring, "Change is not going to stop. Somebody will keep moving the cheese."

As these examples suggest, Who Moved My Cheese? exerts extraordinary power--worth gold in a book--to make readers want to tell others about it and perhaps even buy them a copy. William R. Johnston, president of the New York Stock Exchange, says he found it "a humorous, easy-to-read book for people in the throes of reinventing themselves" and ordered a dozen copies for his staff. Kerry McCluggage, chairman of Paramount Television, encountered the book at a Young Presidents Organization retreat and is getting his local YPO chapter to order copies for all members and their families--90 to 100 copies. The Bank of Hawaii has given 4,000 copies to its staff. Mercedes-Benz has ordered 7,000 copies. Colleen Barrett, executive vice president of Southwest Airlines, liked the book so much she ordered a copy for every employee--27,000 copies. It adds up.

What could possibly account for such popularity? Just a few factors, none of them surprising but all of them powerful. First, the book's topic, change, is of urgent interest to everyone in this time of business revolution, and is so general it can seem relevant to any person or organization. Second, its message--prepare for change, accept it, and enjoy it--is legitimate and worthwhile, if hardly new.

And third, it is simple. How simple? To help place Who Moved My Cheese? in the larger context of business books, here's a typical sentence from Race for the World, a current book on strategy by four McKinsey consultants:

In the specialist model, a company competes across geography by leveraging specialization advantages and intangible scale effects (i.e., leveraging the fixed costs of building intangible assets).

For comparison, here is a typical sentence from Who Moved My Cheese?:

Every day the mice and the littlepeople spent time in the maze looking for their own special cheese.

"I gave it to my 12-year-old daughter," says Dana Williams, Southwest Airlines' director of marketing. "She got it right away." Many others also note the book's appeal to children. Far from feeling defensive, Johnson is proud of the book's simplicity, not just in its prose but also in its message. It fits with what he considers his life's theme: "Sorting through the information overload and reducing it to the few things that make a difference."

One of the book's most unexpected fans is John Kotter, Konosuke Matsushita professor of leadership at the Harvard Business School. As one of America's preeminent business academics, Kotter writes deeply serious books. Yet he speaks of Who Moved My Cheese? with nothing but respect. Why? "People are enormously busy. How do you catch their attention and get them not just to read something but to somehow connect with it in a way that actually helps them do something different? Lots of us in this world would love to do that, my colleagues and I, but the norm we have is to think deeply and to write long, serious books that most people do not have the time or inclination to read."

So, yes, the book is simple--"even ridiculous on one level," says Kotter. "I mean, mice? Littlepeople?" It is short. It is cute. All sins in the world of business books. But as Kotter points out, that is not the bottom line on Who Moved My Cheese? The bottom line, like it or not--and what's not to like?--is this: "He has written something that might actually influence people."