A woman named Rita Beauregard wrote an interesting article a few years ago. It can still be read on archive.org. Here is an excerpt:

The initial strategy

How did De Beers create the diamond brand? And, more importantly, how did it sustain it? De Beers controlled supply and used research-based behavior-change strategies to build demand. And it sustained demand by monitoring its business goals and objectives, as well as market trends, and adjusting its strategies accordingly. Ayers initial strategy was to strengthen the association between diamonds and romance. For young men, they set out to instill the idea that diamonds were a gift of love: the larger and finer the diamond, the greater the expression of love. Similarly, young women were encouraged to view diamonds as an integral element of courtship. 5 Tactics under this strategy included

Within three years of the launch of the first De Beers campaign, diamond sales in the United States increased by 55 percent and an estimated 80 percent of wedding engagements in the country were consecrated with diamond rings.8 Looking back, Ayer noted that the campaign marked a new form of advertising which has been widely imitated ever since. There was no direct sale to be made. There was no brand name to be impressed on the public mind. There was simply an idea the eternal emotional value surrounding the diamond.9 This campaign has been adopted in other things as well. In 1973 a shampoo was specifically created and marketed to be used “every night.” How many people think it is appropriate to wash their hair every day now? Perhaps advertising is forever.