"No man in the world has more courage than the man who can stop after eating one peanut” is credited to American playwright Channing Pollock (1880-1946). His name is associated with the quote as late as 1951—five years after his death—but there is not yet any evidence that he either said or wrote the quotation during his lifetime.
As early as 1899 (when Pollock was only 19 years old), it was written that the prize for self-control “should go to the gent who can eat one peanut and then quit.” There are several citations of the “just one peanut” theme in the 1910s.
Lay’s Potato Chips borrowed this “no one can eat just one peanut” saying with its 1963 advertising slogan of “Betcha can’t eat just one.”
Wikipedia: Channing Pollock (writer)
Channing Pollock (March 4, 1880 - August 17, 1946) was an American playwright, critic and writer of film scenarios.
When the American distribution rights were secured for the German silent film Metropolis, Pollock was hired to write new English-language intertitles for the film. Unfortunately, Pollock chose to delete an entire subplot from the film, concerning the deceased woman who had been married to two of the main characters. (The movie contains shots of a grave bearing the name HEL—a common female name in German—but Pollock felt that American audiences would confuse this with the word ‘Hell’.) The commercial failure of the film’s American release is considered to be largely due to Pollock’s unfortunate decision.
6 February 1899, Warren (PA) Evening Democrat, pg. 2, col. 2:
Any one who can eat one peanut and then stop is possessed of great strength of will or else there are no other peanuts getable.
23 November 1916, Macon (GA) Weekly Telegraph, pg. 4:
...the prize in the great free-for-all self-control sweepstakes should go to the gent who can eat one peanut and then quit.
11 November 1917, Tulsa (OK) World, first section, pg. 16:
They Stand on Every Corner
Some men whom we have heard boast of a good will power cannot eat one peanut and quit.
14 March 1935, Fitchburg (MA) Sentinel, “In New York” by Paul Harrison, pg. 6, col. 4:
Will power, I’ve been told again and again, is the ability to eat just one salted peanut.
21 June 1951, Statesville (NC) Daily Record, “Some Words On Commencement Speeches” by Edward R. Murrow, pg. 8, col. 1:
They might also be reminded in the words of Channing Pollock, that “no man in the world has more courage than the man who can stop after eating one peanut.”
Dictionary of American Maxims
By David Kin and David George Plotkin
Published by Philosophical Library
No man in the world has more courage than the man who can stop after eating one peanut. — Channing Pollock.
14 December 1957, Chillicothe (MO) Constitution-Tribune, pg. 6, cols. 5-6:
Since it takes inhuman self-control to eat just one peanut, about the best thing you can do is pass up the tidbits.
31 October 1960, Dallas (TX) Morning News, section 4, pg. 4:
Perhaps the added consumption was explained by Channing Pollock: “No man in the world has more courage than he who can stop after he has eaten just one peanut.”