David Ogilvy said of Scientific Advertising, "Nobody should be allowed to have anything to do with advertising until he has read this book seven times. It changed the course of my life." In Scientific Advertising Claude C. Hopkins outlines testing and measuring based advertising thereby reducing potential losses of unsuccessful campaigns and maximizing the effectiveness of profitable ones. Or, as Hopkins wrote, the advertiser is "playing on the safe side of a hundred to one shot". Claude C. Hopkins was one of the great advertising pioneers believing that advertising existed only to sell something and should be measurable and justify the results that it produced. Hopkins worked for various advertisers, including Bissell Carpet Sweeper Company, Swift & Company and Dr. Shoop's patent medicine company. Hopkins insisted copywriters researched their client products and produce reason-why copy. He also asserted that a good product was its own best salesperson and as such sampling was an excellent tactic to increase sales.