Get action. Seize the moment. Man was never intended to become an oyster.

Theodore Roosevelt (1858–1919) American politician, statesman, conservationist, writer, US President (1901–1909)

Comment to Mrs. J. A. Roosevelt (25 Dec 1851)
    (Source)

Quoted in David McCullough, Mornings on Horseback (1981), sourced from the W. Sheffield Cowles, Jr. Collection (private). Usually given as a quote in full to his children, McCullough only notes the last sentence ("Man ... oyster") as an actual quotation.