“for once, you believed in yourself. you believed you were beautiful and so did the rest of the world.”

Source: Academy Series - Priscilla "Hutch" Hutchins, Chindi (2002), Chapter 12 (p. 158), quoting Max Stiner

Source: Where I'm Calling From: New and Selected Stories

Australian Idol, Final Performances, Final 4

Attributed to Korda in The Power of Choice (2007) by Joyce Guccione, p. 52, the earliest occurrence of such phrasing yet located is by Martin Lawrence, in "What Up?" in Upscale : The Successful Black Magazine (February 1993), p. 79: "If you don't believe in yourself, then who will believe in you? The next man's way of getting there might not necessarily work for me, so I have to create my own ways of getting there."
Disputed

Interview on The David Frost Show (14 June 1969)
Context: We're trying to sell peace, like a product, you know, and sell it like people sell soap or soft drinks. And it's the only way to get people aware that peace is possible, and it isn't just inevitable to have violence. Not just war — all forms of violence. People just accept it and think 'Oh, they did it, or Harold Wilson did it, or Nixon did it,' they're always scapegoating people. And it isn't Nixon's fault. We're all responsible for everything that goes on, you know, we're all responsible for Biafra and Hitler and everything. So we're just saying "SELL PEACE" — anybody interested in peace just stick it in the window. It's simple but it lets somebody else know that you want peace too, because you feel alone if you're the only one thinking 'wouldn't it be nice if there was peace and nobody was getting killed.' So advertise yourself that you're for peace if you believe in it.

Pearls of Wisdom

Source: The Alchemist