When you think of diamond rings, you probably think of engagements. Diamonds are incredibly rare and valuable, which makes them the perfect stone to include in a piece of jewelry meant to solidify a relationship.

The interesting thing is, they weren’t always perceived this way— if you study the story of how diamond engagement rings came to be popular, you can apply its lessons to your own marketing strategies.

The Engagement Ring Industry

Diamonds were perceived as incredibly scarce up to the late 19th century because they were—until the discovery of gigantic diamond mines in South Africa. These mines flooded the world with an abundance of diamonds, but the businessmen in control of operations knew that the value of diamonds came from their inherent scarcity. Launching the DeBeers cartel, these businessmen controlled the supply of diamonds for decades, working hard to maintain the public perception that diamonds were rare and hard to get.

In addition to manipulating supply, the DeBeers cartel manipulated demand, with a clever and society-changing advertising campaign. In the 1930s, De Beers partnered with the ad agency N. W. Ayer to associate diamonds with romance; they portrayed diamonds, a naturally resilient stone, as a symbol of eternity (“a diamond is forever,” the DeBeers tagline). They convinced young men that the size and quality of the diamond they purchased represented the measure of their love. They convinced young women that they were to expect a diamond at the end of a romantic courtship.

The story was powerful for many reasons. First, it marketed an idea, rather than a product or a brand. They weren’t trying to push diamonds, and they weren’t trying to raise awareness of DeBeers. Instead, they were trying to reshape societal expectations for how marriage proposals worked—and they were successful. Second, it put a cap on the secondary market; because “a diamond is forever,” it’s far less likely to be resold—which means more diamond purchases would be directed toward the original supplier, rather than a third party. Third, it ensured a line of consistent demand, as new generations aged and became ready for marriage.

Today, of course, it’s possible to get conflict-free engagement rings, and the cartel doesn’t have the lockdown on the market it once did—but the general public image of the diamond engagement ring remains.

Key Lessons for Marketers

So what can marketers learn from this trivial historical anecdote?

Perception Matters More Than Reality

Even though diamonds have been much more plentiful and easy to obtain in the past several decades, the public perception that diamonds are rare remains. DeBeers spent a lot of time and effort building up the idea that diamonds were scarce, and that effort has paid off for generations. The same philosophy can be applied to almost any product or concept; for example, charging more for a service can make it seem more inherently valuable, even if you haven’t made any changes to it.

Ideas Are More Powerful Than Brands or Products

While it’s tempting to focus your efforts on marketing a specific product, or showing off your brand to as many people as possible, sometimes it’s better to focus on an idea. Brand and product marketing can be valuable, especially over the course of a long-term campaign, but if you can successfully instill an idea in the public’s mind, that idea can last for generations.

The Right Idea Can Serve Multiple Functions

Further, with the right idea, you can benefit in multiple ways. DeBeers’s marketing of diamond engagement rings increased the public perception of diamond scarcity, encouraged a steady flow of demand, and discouraged resale of diamonds all at the same time. You may not be able to come up with an idea that shapes society to the same degree, but you can get creative when communicating with your target demographics to encourage multiple wanted behaviors simultaneously.

The story of the diamond engagement ring is a marvelous one for businesspeople and marketers to study. It’s a perfect representation of supply and demand as factors for economic development, and a case study of how marketers can control the message and completely reshape public expectations for a given product.