“The problem with the world is that the intelligent people are full of doubts while the stupid one are full of confidence.”

Variant: The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts.

Nobel Prize autobiography (1998)
Context: The world is full of intelligent, well-meaning people who, for one reason or another, did not attend university but are nonetheless well-read and educated. Out there on the prairie lost opportunities of youth were the rule rather than the exception, and I slowly became disabused of the myth of the Bright Young Thing and have not believed in it since.

The Brothers Karamazov (1879–1880)

Arthur Rimbaud.
The Symbolist Movement in Literature (1899)

The lecture in Ashland, Oregon (8th of July 2005)

Quentin "Q" Jacobsen, p. 257
Paper Towns (2008)

Source: Dust Tracks on a Road

Fahrenheit 451 (1953), Coda (1979)
Context: There is more than one way to burn a book. And the world is full of people running about with lit matches. Every minority, be it Baptist/Unitarian, Irish/Italian/Octogenarian/Zen Buddhist, Zionist/Seventh-day Adventist, Women's Lib/Republican, Mattachine/FourSquareGospel feels it has the will, the right, the duty to douse the kerosene, light the fuse. Every dimwit editor who sees himself as the source of all dreary blanc-mange plain porridge unleavened literature, licks his guillotine and eyes the neck of any author who dares to speak above a whisper or write above a nursery rhyme.