“Only the most uncritical minds are free from doubt.”

As quoted in Words from the Wise : Over 6,000 of the Smartest Things Ever Said (2007) by Rosemarie Jarski, p. 312
Context: I doubt if a single individual could be found from the whole of mankind free from some form of insanity. The only difference is one of degree. A man who sees a gourd and takes it for his wife is called insane because this happens to very few people.

Cold Mountain Transcendental Poetry
Context: Today I sat before the cliff
Until the mist and rainbows disappeared
I followed the emerald stream
Explored a thousand tiers of green cliffs
In the morning my spirit rests among white clouds
At night a bright moon floats in the sky
I am free of the busy world
There is not a doubt in my heart or a worry to disturb my mind

"The Iron Fist Behind the Invisible Hand: Capitalism As a State-Guaranteed System of Privilege" (2011)

Speech at the University of California, Berkley, as broadcast by Pacifica Radio (4 January 1969)
1960s

Source: East of Eden

The Satanic Bible (1969)

Choice
The Note-Books of Samuel Butler (1912), Part XX - First Principles

Phillip Vellacott, The Oresteian Trilogy, Penguin 1973 ( Google Books https://books.google.com.au/books?id=tuRiOESBVjkC) <br class="br">Oresteia (458 BC), Agamemnon