Some Notes on Lifemanship (1950) p. 43.
This versatile gambit for disconcerting one's opponent in debate is usually said to have been originated by Potter, even though he had himself said in a footnote to Lifemanship that "I am required to state that World Copyright of this phrase is owned by its brilliant inventor, Mr. Pound". On publication of Lifemanship the critic Richard Usborne wrote to Potter protesting that this stratagem had been invented not by the mysterious Mr. Pound but by Usborne himself, in an article called "Not in the South" published in the May 28, 1941 number of Punch magazine, where the phrase was described as "a formula that let me off the boredom of finding out facts and retaining knowledge". Potter replied, "My God, have I got it wrong? I now perceive with horrifying clearness that I have", but he never corrected the attribution in print. The whole story was set out by Usborne in a letter published in Time magazine, January 5, 1970. http://www.time.com/time/magazine/article/0,9171,943107-4,00.html