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"I'm surrounded by people who are supposed to guide me, and some of them have and others haven't," she said during an inspiring and emotional speech at the first WE Day California event this week.
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"They pressure me: 'You gotta be sexy, you gotta be cute, you gotta be nice, you gotta be all these things.'
"You all have pressure that you deal with everyday," the 21-year-old told hundreds of youngsters during her eight minute address. "With school, with work, with friends, with parents, with family. They tell me what to wear, how to look, what I should say, how I should be.
Selena greets the crowd at the WE Day event
"Until recently I had given into that pressure. I lost sight of who I was. I listened to opinions of people and I tried to change who I am because I thought others would accept me for it. And I realised I don't know how to be anything but me."
Selena, who has an on-off relationship with Justin Bieber, took part in the WE Day conference in Oakland alongside other celebrities, including Orlando Bloom, Seth Rogen and Magic Johnson.
The star posted a backstage photograph of herself alongside Orlando and Seth
WE Day was founded in Canada in 2007, and spread to the US and UK last year. It is an annual youth empowerment event designed to motivate young people to take action on local and global issues.
Backstage, Selena snapped a photo with Orlando, Seth and several other friends. "#Weday – unbelievable time," she captioned the Instagram photo. "So inspired and hopefully encouraged many."
Comedian Seth shared this photo with his fans
Knocked Up star Seth also shared a picture of himself speaking to the crowd, with the caption, "I spoke at #WeDay today and for four minutes I was a good role model to the kids."