This was incorrectly attributed to Nelson Mandela in the movie but is actually by Marianne Williamson (not one of my favorite people, but I love the quote):
"Our deepest fear is not that we are inadequate. Our deepest fear is that we are powerful beyond measure. We ask ourselves, Who am I to be brilliant, gorgeous, talented, fabulous? Actually, who are you not to be? We were born to make manifest the glory of God that is within us. And as we let our own light shine, we unconsciously give other people permission to do the same."