(FORTUNE Magazine) – Most businesses have been working on quality for so long, and with such success, that conventional wisdom now regards quality as a commodity -- the price of admission to global competition rather than what makes you win. Not so, argues Jeremy Main, author of Quality Wars: The Triumphs and Defeats of American Business (The Free Press, $29.95). A distinguished journalist whose many articles in FORTUNE helped define the quality movement, Main urges unrelenting focus on the collection of practices known as TQM, for total quality management. The most successful practitioners of TQM, such as Toyota and Motorola, continue to raise standards for everyone. Although they make products whose defects may soon become too rare to be measured statistically, the two companies remain passionately committed to improvement (Their new goal: perfection.) The cost of low quality can be unbearably high. Main notes that GM wasted much of the $77 billion it invested in its auto business because the company didn't achieve an acceptable standard of quality. The great theme of this book is contained in a quote from a Hewlett-Packard manager: ''Good ideas are often oversold,'' he says, ''and then the world settles down to reality.'' Main presents TQM as a brilliant but oversold idea that has enduring value only when implemented methodically by patient leaders who know exactly what they are doing. Some of the most effective executives in the U.S. -- including Lawrence Bossidy of Allied-Signal and former Tenneco CEO Michael Walsh -- have relied on quality programs as a device to successfully push revolutionary change in their organizations. The author spoons out his observations in highly readable passages focused on the experiences of companies that have been pursuing quality programs for years, including Toyota, Hewlett-Packard, Ford, Motorola, Honda, L.L. Bean, and Milliken. The anecdotal approach brings zest and objectivity to Main's broad summation of the quality movement to date. Readers new to the subject will benefit from his crisp reviews of such basics as statistical process control. Managers who have been working on quality for years will learn from the mistakes and best practices of others. (As Main discloses, the Juran Institute, a consulting firm in Wilton, Connecticut, that specializes in quality, funded his research.) These real-life details and fine writing set Quality Wars apart from the snoozefests that dominate the literature. While discussing Milliken, a leading manufacturer of textiles, Main notes that it took 66 weeks for a collection of threads to become a garment and reach the customer. So much for the timeliness of high fashion! My favorite take-away is the ''five times why'' idea promoted by retired Toyota executive vice president Taichi Ohno. When something went wrong, Ohno urged workers to ask why at least five times. Writes Main: ''You must not be satisfied with knowing that the machine stopped because the fuse blew. Why did the fuse blow? Because the bearing was overloaded. Why was the bearing overloaded? Because it was not lubricated. Why was it not lubricated? Because the lubrication pump was not working properly. Why not? Because the shaft was worn. Why was the shaft worn? Because there was no strainer and scraps of metal got in. After all those whys, you have reached the root cause, and now you know how to stop the problem from recurring.'' You don't need to be a carmaker to benefit from that kind of clear thinking.