“One should be prepared to receive ninety-nine percent of an enemy's attack and stare death right in the face in order to illumine the Path.”

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

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 American: His New Puritanism," http://books.google.com/books?id=tn9HAAAAYAAJ&q=%22If+there+is+one+mental+vice+indeed+which+sets+off+the+American+people+from+all+other+folks+who+walk+the+earth%22+%22it+is+that+of%22+%22that+every+human+act+must+be+either+right+or+wrong+and+that+ninety-nine+percent+of+them+are+wrong%22&pg=RA1-PA87#v=onepage The Smart Set (February 1914)
1910s

As quoted in The Roosevelt I Knew (1946) by Frances Perkins, p. 5
Posthumous publications