“Ninety-nine percent of the world's lovers are not with their first choice. That's what makes the jukebox play.”

Spoken statement (c. 1903); published in Harper's Monthly (September 1932).
Variants:
None of my inventions came by accident. I see a worthwhile need to be met and I make trial after trial until it comes. What it boils down to is one per cent inspiration and ninety-nine percent perspiration.
Statement in a press conference (1929), as quoted in Uncommon Friends: Life with Thomas Edison, Henry Ford, Harvey Firestone, Alexis Carrel & Charles Lindbergh (1987) by James D. Newton, p. 24.
Variant forms without early citation: "Genius is one percent inspiration and ninety-nine percent perspiration. Accordingly, a 'genius' is often merely a talented person who has done all of his or her homework."
"Genius: one percent inspiration and 99 percent perspiration."
1900s
Variant: Genius is one per cent inspiration and ninety nine perspiration.

Source: The Secret

Prayers For The Assassin (2006)

Source: Entwined with You

Source: The Four Pillars of Investing (2002), Chapter 15, A Final Word, p. 297.

Travis McGee series, Dress Her in Indigo (1969)
Context: Any man who outgrows the myths of childhood is ninety-nine percent aware and convinced of his own mortality. But then comes the chilly breath on the nape of the neck, a stirring of the air by the wings of the bleak angel. When a man becomes one hundred percent certain of his inevitable death, he gets The Look.

The Art of Peace (1992)

Source: Wishing I’d Played the Ponies http://takimag.com/article/wishing_id_played_the_ponies/print#axzz3xNaU2RAk, Taki's Magazine, June 16, 2011.