Bieber told Jimmy Fallon that, while he was "disappointed" to have missed some cues during his set, the real reason that tears started to flow was because of the audience's loud applause.
"It was just so overwhelming for me," he told Fallon. "I just wasn't expecting them to support me in the way they did. Last time I was at an awards show, I was booed."
He also clarified that the moment was not staged. "I was just feeling judged and just wanting to win so badly, and just wanting to do what I love so badly that I just put everything on the line," Bieber said. "It was authentic. It was real. I was really wanting it so bad."
After sending his reputation into a downward spiral thanks to a number of run-ins with the law and general bad behavior, Bieber, 21, has been on a quest to remake his image in recent months. And it appears to be working - his latest single, "What Do You Mean?" is currently No. 1 on iTunes.
Bieber also addressed his previous antics on The Tonight Show. "I just had a bunch of knuckleheads around me. I just went through a place of just trying to figure it out," he explained. "You have to test the waters. I just happened to be in the spotlight, in front of cameras all the time, and they caught all those moments."
Watch Bieber's interview here: