“A reliable way to make people believe in falsehoods is frequent repetition, because familiarity is not easily distinguished from truth. Authoritarian institutions and marketers have always known this fact.”

John F. Kennedy: "Remarks on the 20th Anniversary of the Voice of America" (26 February 1962) http://www.presidency.ucsb.edu/ws/index.php?pid=9075&st=&st1=<!-- Online by Gerhard Peters and John T. Woolley, The American Presidency Project -->
1962
Context: We welcome the views of others. We seek a free flow of information across national boundaries and oceans, across iron curtains and stone walls. We are not afraid to entrust the American people with unpleasant facts, foreign ideas, alien philosophies, and competitive values. For a nation that is afraid to let its people judge the truth and falsehood in an open market is a nation that is afraid of its people.

The Deliverance from Error https://www.amazon.com/Al-Ghazalis-Path-Sufism-Deliverance-al-Munqidh/dp/1887752307

As quoted in His Brother's Blood: Speeches and Writings, 1838&ndash;64 https://books.google.com/books?id=qMEv8DNXVbIC&pg=PA199 (2004), edited by William Frederick Moore and Jane Ann Moore, p. 199
1860s, Speech to the U.S. House of Representatives (April 1860)

I Am Running for President in Turkey. From My Prison Cell. (2018)

Source: The Great Crash, 1929 (1954 and 1997 https://openlibrary.org/books/OL25728842M/The_Great_Crash_1929), Chapter V, The Twilight of Illusion, Section II, p. 70

Knowing Yourself: The True in the False (1996)

Mike Wallace interview (4 November 1958), quoted in The Great Quotations (1966) by George Seldes
Other speeches and writings

The Notebooks of Leonardo da Vinci (1883), X Studies and Sketches for Pictures and Decorations

trans. Hollingdale, “Schopenhauer as educator,” p. 153
Untimely Meditations (1876)