“So long as you are a slave to the opinions of the many you have not yet approached freedom or tasted its nectar”

Dienekes p. 60
Gates of Fire (1998)
Source: Gates of Fire: An Epic Novel of the Battle of Thermopylae

Radio address "Our American Culture" broadcast during an intermission of the Metropolitan Opera. (1 March 1941)
Context: Once a man has tasted freedom he will never be content to be a slave. That is why I believe that this frightfulness we see everywhere today is only temporary. Tomorrow will be better for as long as America keeps alive the ideals of freedom and a better life. All men will want to be free and share our way of life. There must be so much that I should have said, but haven't. What I will say now is just what most of us are probably thinking every day. I thank God and America for the right to live and raise my family under the flag of tolerance, democracy and freedom.

Über den Umgang mit Menschen (1788)
Context: Do not be too much a slave of others' opinions of you! Be self-sufficient! Why, in the end, does the opinion of the whole world trouble you, if you do what you should?

“In these great times,” Harry Zohn, trans., In These Great Times (Montreal: 1976), p. 74

Book I, sec. 17
History of Rome

This quotation was first used in print (and misattributed to Leonardo da Vinci) in a science fiction story published in 1975, The Storms of Windhaven. One of the authors, Lisa Tuttle, remembers that the quote was suggested by science fiction writer Ben Bova, who says he believes he got the quote from a TV documentary narrated by Fredric March, presumably I, Leonardo da Vinci, written by John H. Secondari for the series Saga of Western Man, which aired on 23 February 1965. Bova incorrectly assumed that he was quoting da Vinci. The probable author is John Hermes Secondari (1919-1975), American author and television producer.
Misattributed
Variant: For once you have tasted flight you will walk the earth with your eyes turned skywards, for there you have been and there you will long to return.

A liberdade é a possibilidade do isolamento... Se te é impossível viver só, nasceste escravo.
The Book of Disquietude, trans. Richard Zenith, text 283

Source: 1850s, Letter to Henry L. Pierce (1859), p. 377

Speech delivered to the Bombay Presidency Mahar Conference (31 May 1936)