Respectfully Quoted: A Dictionary of Quotations. 1989.
Benjamin Disraeli (180481)
The secret of success is constancy of purpose.
BENJAMIN DISRAELI, speech at banquet of National Union of Conservative and Constitutional Associations, Crystal Palace, London, June 24, 1872.Selected Speeches of the Right Honourable the Earl of Beaconsfield, ed. T. E. Kebbel, vol. 2, p. 535 (1882).