Courage is the ladder on which all the other virtues mount.
Clare Boothe Luce (1903-1987) American dramatist, diplomat, politician
“Is the New Morality Destroying America?”, speech, IBM Golden Circle Conference, Honolulu (28 May 1978)
(Source)
The speech was first published in The Human Life Review, Vol. 4 (1978). Then the quotation was extracted in "Quotable Quotes," Reader's Digest (May 1979), which is the most common citation.
More discussion about this quotation: The Big Apple: “Courage is the ladder on which all the other virtues mount”.
