AceShowbiz -

Justin Bieber sheds a tear in the first trailer for his second documentary film "Justin Bieber's Believe". The Canadian pop star talks about dealing with critics, answers a question about being a possible next "train wreck," discusses his love life, and jokes about his shaggy pants.

"When you've reached a certain point in your life, there are people out there waiting to see you fall," says the 19-year-old singing sensation. "But rather than let gravity take you down, sometimes you have to take matters into your own hands and fly."

A scene which shows his infamous altercation with a paparazzo in London is shown when he's confronted by director Jon M. Chu who says, "We've seen it time and time again. Young stars reach the top only to fall. Are you aware that you could be the next train-wreck?"

"I really wanted to hit him," he admits. "That's what they wanted. I learned from that." He continues, "You always gotta keep a smile on your face, it's all about positivity."

At one point, the "Hearbreaker" singer seems to address his very public on/off relationship with Selena Gomez as he gloomily says, "When you fall in love, when you break up."

His manager Scooter Braun and former mentor Usher come to Bieber's defense insisting it is tough growing up under media scrutiny. "You can't have a normal life if you're a superstar," Usher says. "He's forced to grow up in front of the world."

The movie will arrive in theaters across the U.S. on Christmas Day.