“Most police work boils down to minimizing the impact on society of stupidity; of the remainder, the overwhelming majority is about malice and deliberate evil, but it’s still almost all stupid.”

Murphy's Law Book Two : More Reasons Why Things Go Wrong! (1980) ISBN 0843106743 by Arthur Bloch page 52.
This statement has often been referred to as Hanlon's Razor, though the author himself has remained relatively unknown, and some theories arose that "Hanlon" might have been a corruption of "Heinlein". Hanlon actually was a winner in a contest to come up with further statements similar to "Murphy's Law", for publication in this particular book. This phrase or very similar statements have also been attributed to William James, Napoleon Bonaparte, Richard Feynman (who might well have quoted it) and others.
Similar statements have been made by Goethe, and indeed, Robert Heinlein:
In The Sorrows of Young Werther Goethe declared, "Misunderstandings and neglect occasion more mischief in the world than even malice and wickedness. At all events, the two latter are of less frequent occurrence."
In his story Logic of Empire (1941) Heinlein declares: "You have attributed conditions to villainy that simply result from stupidity". He calls this the "devil theory" of sociology. His character Lazarus Long also voices a variation on the theme in the novel Time Enough for Love: "Never underestimate the power of human stupidity."
Variants of the phrase which have been variously attributed to this wide assortment of authors include:
Never ascribe to malice that which can be adequately explained by stupidity.
Never ascribe to malice that which can be explained by incompetence.
Never ascribe to malice that which is adequately explained by stupidity.

The Bonhoeffer Reader https://www.google.com/books/edition/The_Bonhoeffer_Reader/CNZgAwAAQBAJ?hl=en&gbpv=1&pg=PA766, p. 766
Letters and Papers from Prison (1967; 1997), On Stupidity

Graduation Exercises at the United States Military Academy at West Point, New York, U.S. (3 June 1947) http://www.eisenhower.archives.gov/all_about_ike/quotes.html
1940s
Context: War is mankind's most tragic and stupid folly; to seek or advise its deliberate provocation is a black crime against all men. Though you follow the trade of the warrior, you do so in the spirit of Washington — not of Genghis Khan. For Americans, only threat to our way of life justifies resort to conflict.

Tomorrow and Tomorrow and Tomorrow (1952)
Source: Complete Essays 1, 1920-25

Source: Maybe, Maybe Not

Source: The Wizard of Ooze

Reflections