James Matthew Barrie? Apocryphal?
Dear Quote Investigator: The Scottish playwright and novelist J. M. Barrie created the beloved fictional world of Peter Pan and Wendy. He also offered cogent advice about not ascribing excessively malign intentions to your antagonists. Are you familiar with this saying? Do you know when it was spoken?
Quote Investigator: In 1922 James Matthew Barrie delivered the Rectorial Address at the University of St Andrews in Scotland. His speech included a guideline with a humorous edge for assessing other people’s thoughts. Emphasis added to excerpts by QI:[ref] 1922, Courage by J. M. Barrie, The Rectorial Address Delivered at St. Andrews University on May 3, 1922, Quote Page 9 and 10, Charles Scribner’s Sons, New York. (Google Books Full View) link [/ref]
I urge you not to use ugly names about anyone. In the war it was not the fighting men who were distinguished for abuse; as has been well said, “Hell hath no fury like a non-combatant.” Never ascribe to an opponent motives meaner than your own.
Below are additional selected citations in chronological order.
The saying together with a precise citation was included in the 1949 edition of “The Home Book of Quotations: Classical and Modern” selected by Burton Stevenson:[ref] 1949, The Home Book of Quotations: Classical and Modern, Selected by Burton Stevenson, Sixth Edition, Section: Purpose, Quote Page 1660, Dodd, Mead and Company, New York. (Internet Archive at archive.org) [/ref]
Never ascribe to an opponent motives meaner than your own.
J. M. BARRIE, Rectorial Address. St. Andrew’s, 3 May, 1922.
In 1952 the prominent newspaper columnist Franklin Pierce Adams included the quotation ascribed to Barrie in his compilation “FPA Book of Quotations”.[ref] 1952, FPA Book of Quotations, Selected by Franklin Pierce Adams, Section: Purpose, Quote Page 665, Funk & Wagnalls Company, New York. (Verified on paper)[/ref]
In 1980 a thematically related general statement ascribed to Robert J. Hanlon appeared in the compilation “Murphy’s Law Book Two: More Reasons Why Things Go Wrong”:[ref] 1980, Murphy’s Law Book Two: More Reasons Why Things Go Wrong, Compiled and Edited by Arthur Bloch, Quote Page 52, Price/Stern/Sloan Publishers Inc., Los Angeles, California. (Verified with scans)[/ref]
Never attribute to malice that which is adequately explained by stupidity.
The above adage is called “Hanlon’s Razor”, and it was further examined in the website article here.
In conclusion, J. M. Barrie should be credited with the statement in his 1922 speech.