Industry could not benefit from its increased productivity without a substantial increase in consumer spending. This contributed to the development of mass marketing designed to influence the population's economic behavior on a larger scale. In the 1910s and 1920s, advertisers in the U.S. adopted the doctrine that human instincts could be targeted and harnessed – "sublimated" into the desire to purchase commodities. Edward Bernays, a nephew of Sigmund Freud, became associated with the method and is sometimes called the founder of modern advertising and public relations. Bernays claimed that:"general principle, that men are very largely actuated by motives which they conceal from themselves, is as true of mass as of individual psychology. It is evident that the successful propagandist must understand the true motives and not be content to accept the reasons which men give for what they do."In other words, selling products by appealing to the rational minds of customers (the main method used prior to Bernays) was much less effective than selling products based on the unconscious desires that Bernays felt were the true motivators of human action. "Sex sells" became a controversial issue, with techniques for titillating and enlarging the audience posing a challenge to conventional morality.