Pilnmēness nogurdinātie - Mythbusting

The tradition of the diamond engagement ring was largely concocted in the 1930s by De Beers's ad agency N.W. Ayer & Son -- the same Madison Avenue shop that would later craft the wildly successful slogan "A diamond is forever." Through magazine advertisements and Hollywood product placements, American customers were sold the idea that even a man of modest means must give a diamond to his betrothed, just as kings and aristocrats had done in several examples cherry-picked from European folklore.

In fact, diamonds historically served as tokens of statist privilege more than anything so frilly and ordinary as love. De Beers's appeal to royal fantasies (and, more subtly, male fears of inadequacy) nonetheless caught the American public's imagination, as did the notion that a groom is supposed to spend two months of his salary on a rock. This, too, was an invented custom. It was also flexible: In ad blitzes elsewhere, British customers were told to spend one month's salary, while the Japanese were told to spend three.
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The resale value of a diamond drops between 30 and 50 percent the moment you walk out of the store with it (a sixth myth is that they are good investments; they aren't) so you might as well enjoy its illusory light while you can.
// Five Myths About Diamonds, Washington Post