Avril Lavigne’s origin story would be the perfect American fairytale if it wasn’t so undeniably Canadian. She grew up in Napanee, Ontario, a small town best known for its proximity to the country’s largest highway and its selection of fine truck stops. She sang Pentecostal hymns in her family’s church and performed in local productions of Godspell and You’re a Good Man, Charlie Brown. It was little more than an average, provincial life.

When the nearest big-city country station held a singing contest, a 14-year-old Lavigne sent in a tape for a chance to sing with none other than Shania Twain, the Canadian country-pop superstar. Lavigne didn’t just acquit herself: She won the damn thing, which meant driving two-plus hours to the nation’s capital and belting Twain’s brassy 1993 hit “What Made You Say That” in front of a packed Ottawa hockey arena. At the time, Lavigne told Twain she wanted to be “a famous singer.”

Lavigne had no idea how quickly her dream would come true: Within a few years, she’d be sneering on the cover of Rolling Stone in a black tank top and a curt plaid skirt, winkingly labeled “the Britney slayer.” The onetime country-pop princess who performed hits by Faith Hill and Sarah McLachlan at an early record label audition had become a gleeful anarchist, a pop-punk supernova who skated through videos for hits like “Complicated” and “Sk8er Boi,” causing chaos in ratty T-shirts and neckties. She wasn’t disingenuous or calculating; she was a teenager, one whose formative experiences and changes in taste were taking place while she navigated the expectations that come with a major-label record deal. The reaction between Lavigne’s volatile energy and the music industry’s commercial imperative produced her 2002 debut Let Go, a rebuttal of Spears-Aguilerian pop—overtly sexual, vaguely urban, hyper-processed—churned out by the exact same kind of hit factory. It boasts a handful of genre-changing smashes and mood swings that’d put a high school sophomore to shame.

While Lavigne’s ascent from local radio contests to the top of the charts seems rapid in retrospect, her career took shape in fits and starts. Nine months after she appeared on stage with Twain, Cliff Fabri—the manager who shepherded her through the earliest phase of her career—watched her sing country karaoke in a Kingston, Ontario Chapters, the Canadian equivalent of being discovered in a college town’s Barnes & Noble. “I was thinking of her as another Sheryl Crow. They both had the same small-town roots,” Fabri told The New York Times in 2002. “Then I was thinking Fiona Apple, because of her independence. She definitely had attitude. So my line was Sheryl Crow meets Fiona Apple.”

By the summer of 2000, Lavigne was a known commodity within the small Canadian music industry, with executives driving up to Napanee to hear her sing in her parents’ basement. Lavigne spent that summer and fall heading back and forth between Napanee and Manhattan working on a development deal, and she was bold enough to ask her high school principal for course credit given the time she was spending in the studio. Within a few months, she’d accrued enough buzz to score an audition for L.A. Reid, then the president of Arista. A few hours after singing for Reid, Lavigne and her team were scooped up by a limo and whisked to the top of the World Trade Center to celebrate her lucrative, major-label record deal.

While Arista was prepared to invest significant time and money in Lavigne—Fabri told the Toronto Star she’d signed a two-album deal for over $1 million—she was struggling to find an appropriate sound. Inspiration didn’t strike until Lavigne traveled to Los Angeles in May 2001, where she worked with journeyman songwriter Clif Magness. The first song they wrote together was “Unwanted,” an angsty, crunchy statement of purpose that suggested Lavigne was more interested in meathead riffage than contemporary Nashville sparkle. (They also came up with roaring album opener “Losing Grip,” which beat Evanescence to the nu-metal-pop punch by a solid year.) Lavigne had finally settled on an aesthetic that satisfied her evolving taste, but her label was aghast that their new signee—still barely old enough to drive—was veering into heavy alt-rock. “Arista was drop-dead shit afraid that I would come out with a whole album that sounded like ‘Unwanted’ and ‘Losing Grip,’” Lavigne told Rolling Stone in March 2003. “I swear they wanted to drop me.”

When they sent her back into the studio, they paired her with Lauren Christy, Graham Edwards, and Scott Spock, a production team that worked together under the extremely aughts name the Matrix. “We’d been listening to the kind of stuff she had been doing—it had a Faith Hill kind of vibe,” said Christy in a 2006 interview. “As soon as she walked in the door we knew this was just wrong. This kid had melted toothbrushes up her arm, her hair was in braids and she wore black skater boots. She didn’t seem like the Faith Hill type.” They played Lavigne a song written in the style of her earlier demos, and she hated it. When they heard “Unwanted,” they scrapped their work and went back to the drawing board. Lavigne and the Matrix came together the very next day and wrote “Complicated,” the song that made her a teen icon.

The exact division of labor behind “Complicated” remains a point of contention. When Lavigne spoke to Rolling Stone in 2003, she insisted that she was the primary author; the Matrix argued that her contributions were far less substantial. “Avril would come in and sing a few melodies, change a word here or there,” Christy told Rolling Stone. “She came up with a couple of things in ‘Complicated,’ like, instead of ‘Take off your stupid clothes,’ she wanted it to say ‘preppy clothes.’” When asked to comment, L.A. Reid opted for poptimism through an executive’s lens. “If I’m looking for a single for an artist, I don’t care who writes it,” Reid told Rolling Stone.

No matter where the song falls on the authenticity spectrum, “Complicated” is the teenage state of mind: a hissing, bubbling cauldron of anger, confusion, naïveté, lust, paranoia, and desperation. It’s a moment in time where you’re childlike enough to beg for a simple explanation for everything and just mature enough to know there’s no such thing. (Maybe you’d neg a friend by saying, “Chill out, what you yelling for?” and then scream at the top of your lungs a few seconds later.) It’s a phase where you can barely understand your own behavior, let alone anyone else’s, and the quality that set Lavigne apart from peers like Michelle Branch and Vanessa Carlton—singer-songwriters mining the same musical and emotional terrain—was her ability to imbue her music with the thrill and terror of real teenhood.

The song echoes throughout the rest of Let Go: Lavigne’s need for clarity and authenticity, her struggle to find solid ground, her general distaste for the bourgeois tyranny of polo shirts. It also sounds incredible, in part because the Matrix understood that Lavigne could sing with enough defiance to camouflage their clear, starry-eyed pop melodies. After opening with some lazy record-scratching and the brightest, bluest chords this side of “Free Fallin’,” “Complicated” locks into a military structure: twinkling keyboards, tight drum loops, a teasing vocal hook that can still send a karaoke bar into a frenzy. Everyone involved knew it was a hit right away, and when Reid heard it he sent Lavigne back to the Matrix to bang out a dozen songs just like it.

Lavigne felt conflicted about her work with the Matrix—they ended up contributing five songs to Let Go, the same number as Magness—and was practically disowning it while Let Go was still flying off of store shelves. “I don’t feel like ‘Complicated’ represents me and my ability to write,” she confessed to Rolling Stone. “But without ‘Complicated,’ I bet you anything I wouldn’t have even sold a million records. The songs I did with the Matrix, yeah, they were good for my first record, but I don’t want to be that pop anymore.” She’d finally figured out what kind of music she wanted to make, only to be told it wasn’t meeting expectations. Being painted as another teen pop star fresh off the assembly line just added insult to injury.

Her sense of grievance aside, the songs Lavigne made with the Matrix are Let Go’s indisputable highlights, striking a perfect balance of scrappy attitude and radio-ready polish. Second single “Sk8er Boi” is Lavigne at her most pugnacious, snarling the chorus in tight harmony with herself over power chords that sound like they’ve been popped in the microwave until sizzling. It’s also the album’s most developed example of storytelling, though that isn’t saying much: A high school beauty queen can’t appreciate her local diamond in the rough, and she’s left to watch him rock out on MTV with a triumphant Lavigne by his side while she nurses her baby in suburban hell. It sounds like Taylor Swift’s “You Belong With Me” as if written by a normal teenager instead of a precocious musical cyborg.

She took her first stab at a power ballad on “I’m With You,” a desperate, string-backed plea for companionship that sounds like a late-’90s Aerosmith B-side. And Let Go’s hidden gem is “Anything but Ordinary,” a coming-of-age anthem with a melody like pure spring water. (It’s also the one song on the album that tests your suspension of disbelief with its lyrics—listen and hear Lavigne describe the world as “A beautiful accident/Turbulent, succulent/Opulent, permanent” in the bridge.) L.A. Reid would’ve made it the album’s title track if Lavigne hadn’t intervened. She’d already been forced to subjugate her instincts. Couldn’t she just name the album?

Let Go’s phenomenal success—it’s been certified platinum seven times over in the U.S. alone—may not have single-handedly slayed Britney Spears, but it helped make room for songs reliant on alternative palettes. As the teen-pop stars of the late ’90s leaned into hip-hop, R&B, and electronic influences, Lavigne and her contemporaries filled the resulting vacuum with pop melodies and punk attitude. The Matrix quickly landed on a formula—clean, spiky riffs, punchy live drums, sparkling background atmospherics—that yielded minor hits for then-Disney icon Hilary Duff and indie legend Liz Phair, both making bids for mainstream success. It wasn’t long before up-and-coming stars like Duff, Ashlee Simpson, and Lindsay Lohan adapted the same formula. Lavigne spawned enough imitators for The Globe and Mail to put together “Pieces of Avril,” a 2004 trend piece cataloguing the would-be sk8er girls—Fefe Dobson! Katy Rose! Skye Sweetnam!—emerging in her wake. This wasn’t a phenomenon limited to female artists, either: Pop-punk boy bands like Good Charlotte, Simple Plan, and Yellowcard landed on the charts with slightly chunkier riffs and whiny, exasperated vocals.

Her influence continued to trickle down through the Disney talent pipeline—Hannah Montana wouldn’t exist without “Sk8er Boi” as a template—and even Taylor Swift, who ended up becoming the country-pop ingenue Arista thought they’d found with Lavigne. Lavigne herself earned a co-writing credit on “Breakaway,” the title track on Kelly Clarkson’s 2004 album of the same name. Of course, Breakaway is best remembered for “Since U Been Gone,” the song that launched Clarkson’s career, revitalized Max Martin’s, and quickly entered the contemporary pop canon. And while Martin and Dr. Luke have credited the Yeah Yeah Yeahs’ “Maps” for inspiration, it’s hard to imagine “Since U Been Gone” becoming a massive hit without Lavigne clearing the path.

Let Go is still rippling through the musical pond today: When asked about Lavigne for a Billboard cover story earlier this year, next-generation indie heavyweights like Soccer Mommy, Alex Lahey, and Snail Mail—who said “I just wanted to be her so badly”—credited her as a role model, a teenage girl whose stardom was built on videos spent trashing the mall and songs about guys who break your heart by smoking too much weed. And yet, since her debut, Lavigne has never struck gold in the same way, veering back and forth between surly post-grunge (2004’s sophomore effort Under My Skin) and songs like “Girlfriend,” a bratty 2007 collaboration with Dr. Luke that hit No. 1 but felt like a concession. Listening to later singles like “Here’s to Never Growing Up” and “17” feels like chewing pieces of dime-store bubblegum when you’re old enough to make your own appointments at the dentist.

Lavigne has spent the last few years fighting back from Lyme disease and navigating the end of her marriage to Nickelback frontman Chad Kroeger, and her impending pivot into Christian music—judging by recent single “Head Above Water,” her first in half a decade—is a full-circle return to her religious, small-town roots. Let Go is the foundation of her surprisingly considerable legacy. Her feelings about it might be, well, complicated: She’d grown up enough by its release to know it wasn’t the album she wanted to make, and she never quite escaped its shadow. But you can imagine her listening to Let Go like she’s flipping through a yearbook or watching some long-forgotten DVD from a high-school talent show. It feels like a true dispatch from the frontlines of a teenager’s brain: unsure of itself, inelegant and occasionally inane, crackling with nervous energy.