Quoted from his first book https://en.wikipedia.org/wiki/Success_and_Failure_Based_on_Reason_and_Reality, "Success and Failure Based on Reason and Reality" https://www.amazon.co.uk/SUCCESS-FAILURE-BASED-REASON-REALITY/dp/9970983903/ on Amazon, P.104 (July 2018)
Related quotes
Never Scared (HBO, 2004)
Song lyrics, The Red Shoes (1993)
Speaking with reporters on April 9, 1962 at F.O.E.'s Welcome Home Dinner; as quoted in "Sidelights on Sports" by Al Abrams, in The Pittsburgh Post-Gazette (Wednesday, April 11, 1962), p. 24
Baseball-related, <big><big>1960s</big></big>
“If you don't believe in yourself, then who will believe in you?”
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
Source: Everybody’s Autobiography (1937), Ch. 2
“You cannot believe in God until you believe in yourself.”
Pearls of Wisdom
Asked whether things are meant, while been interviewed by The Independent on Sunday, May 25, 2003 http://findarticles.com/p/articles/mi_qn4159/is_20030525/ai_n12738402