The pumpkin spice latte, Starbucks’ most iconic and popular seasonal drink, almost didn’t happen. “A number of us thought it was a beverage so dominated by a flavor other than coffee that it didn’t put Starbucks’ coffee in the best light,” says Tim Kern, who recently left Starbucks after 20 years, and who started at Starbucks when it was a regional chain of just six stores.

This year, Starbucks celebrates the tenth anniversary of the drink, which now goes by the “PSL” shorthand, and has its own hashtag on Twitter. The flavor itself is now so popular that incidence of “pumpkin spice”—that distinctive mix of pumpkin, nutmeg and cinnamon—in food served by restaurants increased 234% from 2008 to 2012. It’s everywhere in the US, from air fresheners to tortilla chips, and the drink itself has been copied by Dunkin’ Donuts, McDonald’s and home chefs.

It’s the ease with which this drink can be copied—it’s just pumpkin spice “sauce” and coffee—that had Kern worried when he first encountered the prototype. “It was a great business idea, but it was also easy to imitate—easier to imitate than the taste of a great espresso,” says Kern. “Everyone can put a pumpkin spice syrup in whatever they want.”

Kern’s account of the genesis of the PSL is corroborated by Peter Dukes, who was part of the team that developed the drink. “It wasn’t the natural winner, but there was something there,” he told the Wall Street Journal. Both chocolate caramel and cinnamon spice came out ahead of pumpkin spice flavor, which invites all kinds of counterfactual thinking—what seasonal flavor of M&M’s would Target be proud to have an exclusive on had things gone differently and it wasn’t pumpkin spice?

Pumpkin spice is by now such an institution that it is becoming a year-round phenomenon. Consumers like it because it suggests “native American, locavore, retro-comfort,” said Anton Angelich, a vice president at flavor-extract company Virginia Dare. Starbucks readily admits that there is no actual pumpkin in the PSL, and that’s final. “If we changed the recipe now, we’d have a revolt,” said Dukes.