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Delia’s was the canary in the coal mine of teen-girl retail. The iconic 1990s clothing brand first flourished through its ubiquitous catalogs, which put inexpensive, of-the-moment clothes such as babydoll dresses and baggy jeans into the wardrobes of American adolescents. Then, in the 2000s, Delia’s became a physical place: The company opened more than 100 stores in suburban shopping malls, eventually reaching 33 states. By the end of 2014, however, Delia’s was done—bankrupt, with its stores closed and its catalog out of print.

Many of Delia’s mall competitors soon succumbed to similar fates. Wet Seal, Quiksilver, Pacific Sunwear, Aéropostale, The Limited, Rue21, Papaya, Claire’s, and Charlotte Russe have all since filed for bankruptcy protection. Many other retailers have closed stores, changed strategies, or restructured businesses. Earlier this week, after months of speculation, one of teen apparel’s biggest power players joined that ignominious club: Forever 21 filed for bankruptcy. The store plans to close hundreds of locations and cease operations in dozens of countries in an effort to save the business.

There’s no single reason that so many stalwarts of the American mall have fallen on such hard times. Shopping-center foot traffic has been on the decline. Internet commerce is ballooning in popularity. Some mall retailers expanded too quickly and have real-estate and inventory albatrosses around their necks. Some just make stuff people don’t really want. But for teen-focused retailers like Forever 21, whose businesses have sputtered in a time when kids are primed to shop from the first moment they clutch their mother’s smartphone, one miscalculation looms large. Those mall stores helped seal their own fates by underestimating the sophistication and resourcefulness of young people.

Since its rapid expansion in the early 2000s, Forever 21 has been among the quickest and dirtiest participants in the quick and dirty “fast fashion” business that has come to dominate the American apparel market. Fast fashion is what it sounds like: Global behemoths such as Zara and H&M have built massive, highly efficient supply chains in which low-wage garment workers turn cheap textiles into of-the-moment clothing that’s distributed around the world as quickly as possible and sold for next to nothing. At Forever 21, a tank top costs as little as $2.90. The brand’s average store has grown to nearly 40,000 square feet—more than 30 percent bigger than the average Best Buy. That’s a lot of cheap tank tops.

The constant novelty of Forever 21 proved especially enticing to Millennials, who were in their teens and early 20s in the 2000s. For them, walking into a Forever 21 became the teen-retail equivalent of entering a casino: a cavernous, disorienting chamber of sequins and patterns and forbidden pleasures. Instead of booze and gambling, the vices offered were more kinds of $12 Daisy Dukes than a 15-year-old in 2006 could have imagined. Forever 21, like its fast-fashion compatriots Zara and H&M, succeeded because it gave young people the thrill of personal choice, more so than any other business model in the world. It crippled some of those other models in the process.

Now, Forever 21 is in trouble for exactly the same reason as the stores it out-muscled: It’s being beaten at its own game. Unlike Millennials, who were compelled by the abundance of Forever 21 and saw its wares as an opportunity to better adhere to existing trends, Generation Z consumers—kids currently in grade school and college—just see a bunch of cheap stuff that everyone already knows about. The familiar is a hard sell to today’s young shoppers, according to Thomai Serdari, a fashion-branding strategist and marketing professor at New York University. “A big difference with Generation Z is that they’re not all trying to look the same,” she says.

Previous generations of consumers “were not as informed,” says Serdari. Gen Z “likes to do research, they have a limited budget, they spend online because they can get better deals.” In other words, being large, cheap, and geographically convenient—Forever 21’s main selling points—are no longer impressive to a huge proportion of its market, even if Forever 21 believes it has the capacity to clothe the goths, the punks, and the VSCO girls.

As young people have rapidly become more digitally adept and more constantly connected, online-only fast-fashion retailers like FashionNova and ASOS and smaller specialty brands like Brandy Melville have chipped away at Forever 21’s consumer base with more sophisticated branding, better use of social media, and a better understanding of design trends. They’re also not weighed down by Forever 21’s brick-and-mortar leases for more than 700 stores across the globe, which are widely cited as the biggest practical barrier to the company’s return to profitability.

Forever 21 declined to comment on its future plans, but in an interview with The New York Times, executives said that in addition to closing some stores, the company would seek to renegotiate other leases with malls, many of which are eager to retain large retailers. Forever 21 also still has excellent name recognition among young shoppers, and the company claims that as much as 40 percent of its clientele is between 25 and 40—a group of people whose shopping habits are better understood by the corporations selling to them. Still, Serdari says that older shoppers tend to follow along with what younger people do, which means many people over 25 are likely adopting Gen Z’s tactics as we speak.

A desire for individuality isn’t the only thing driving young people away from mall retailers, according to Serdari. “We have a new generation that is more sophisticated in the sense that they are more interested in what they’re consuming,” she says. “They have strong convictions about what they should be wearing and the ethical and authenticity aspects of it, and transparency in terms of manufacturing—especially the ones that are really concerned about climate change.” She pointed to Greta Thunberg and the success of her recent student climate protests as an indicator of what Generation Z is willing to do in order to stand up for their beliefs.

For some young consumers, those beliefs mean eschewing fast fashion—a business shot through with ethical, environmental, and human-rights problems—in favor of buying clothes secondhand. Teens have been gifted thrifters for generations, but start-ups like Depop have turned that facility into something that can be done on a far larger scale. These start-ups allow young people to buy used clothing from each other and scour the internet for weird finds from the backs of strangers’ closets. Coming up with a real Guns N’ Roses tour shirt is far more of a triumph than buying a reproduction off the rack at the local mall—plus, no one else at school will have it.

Depop has become so popular with young people that the app is now its own social-media ecosystem, complete with its own entrepreneurial success stories and breakout stars. That growth, along with all the other ways that the internet lets teens explore identities and aesthetics for themselves and find things they like, has started to change how fashion trends form in and of themselves. “It’s now much more common to see trends growing from the bottom up, and then the press catches on to them, and then they become mass-marketed,” says Serdari.

This time, though, the winner isn’t a business, but young people themselves, who have outsmarted the very businesses that used to be so good at raiding the paychecks from their summer jobs. Before social media—and particularly before Instagram, which is massively popular among American adolescents—fast-fashion retailers could crib from luxury designers and deposit their own spins on high-end trends in stores before price-conscious consumers could know what was coming. Now, by the time Forever 21 catches on to something, even its quick supply chain might not be enough to satisfy people who have already known about a trend for weeks.

It might be social media, not online shopping itself, that presents the biggest problem for Forever 21 as it moves forward. Young Americans have the most direct window into the lives of others that they’ve ever had, which means they’re acutely aware of how people shop, and any particular marketer’s ability to influence their decisions is limited by the fragmented, decentralized way that adolescents learn about the world.

Gen Z isn’t brand-loyal, according to Serdari, and why should they be? Forever 21 might have taken choice and affordability to its logical extreme within the confines of a shopping mall, but no one clothing company can compete with the internet itself—and the resourcefulness of the people born into using it.

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