I know of no such unquestionable badge and ensign of a sovereign mind as that of tenacity of purpose. . .
Source: In The Ultimate Success Quotations Library, 1997.
-- Ralph Waldo Emerson, (May 25 1803-1882), US philosopher, poet, essayist; He was the main spokesman of his time for moral optimism and belief in the individual: Self-Reliance, 1844.