At Sunday's Grammy Awards, a relatively obscure Montreal-based indie rock band pulled off a upset that's being called both "shocking" and "puzzling." The band, Arcade Fire, which many online protesters say they'd never heard of before the event, beat out major commercial artists like Lady Gaga, Eminem, and Katy Perry to win the Grammys' top prize: Album of the Year. What happened? (See Arcade Fire accept their award and play a song)

1. There's an indie precedent
Arcade Fire isn't the first indie act to break through this way, says August Brown in the Los Angeles Times. Its career arc resembles U2 and Radiohead's growth from indie darling to chart-topper. Unlike those groups, however, Arcade Fire has remained on an small label and hasn't had "any smash individual singles."

2. The Suburbs is just a great album
In a market dominated by singles, Arcade Fire's The Suburbs is a great "cohesive and heartfelt full-length" album, says Mike Orme in SF Weekly. It seems the Academy elected to recognize and reward this, despite the album's "relative lack of mainstream ubiquity."

3. Arcade Fire had momentum
The big win "capped off a huge year for Arcade Fire," says Jacob Ganz at NPR. Not only did their album debut at No. 1 on the Billboard charts, the band also sold out three nights at Madison Square Garden. "The award should give the band an even bigger boost."

4. They've long been a critical darling
While Arcade Fire lacks the "mainstream recognition of Eminem or Lady Gaga," the band had been one of "the most lauded groups in rock" since their 2004 debut, Funeral, says Tris McCall in The Star-Ledger. Likewise, The Suburbs garnered critical praise for "its energy, its scope, and its sharp hooks."

5. Indie is in
"Maybe it was the indie thing," says Ganz. While name pop singers ruled the charts this past year, they didn't rule The Grammys. In another of the night's major upsets, jazz bassist-singer Esperanza Spalding beat out high-profile acts like Justin Bieber and Drake to nab the Best New Artist trophy.

6. They split the vote
"The heavy-hitter vote was divided," theorizes an incredulous Win Butler, Arcade Fire's lead singer, as quoted by MTV News.  It "never even crossed my mind" that we could win, but maybe we got the underdog vote. "People love underdog movies."