“He that has once done you a kindness will be more ready to do you another, than he whom you yourself have obliged.”
Franklin himself calls this an "old maxim" when he repeats it at page 48 http://www.ushistory.org/franklin/autobiography/page48.htm of his autobiography.
Franklin's recognition of this effect caused it to be named after him. Wikipedia, Ben Franklin Effect https://en.wikipedia.org/wiki/Ben_Franklin_effect.
Misattributed
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Benjamin Franklin 183
American author, printer, political theorist, politician, p… 1706–1790Related quotes

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Letter to Marin Mersenne (July 27, 1638) as quoted by Florian Cajori, A History of Mathematics (1893) letter dated in The Philosophical Writings of Descartes Vol. 3, The Correspondence (1991) ed. John Cottingham, Robert Stoothoff, Dugald Murdoch

"American SF and The Other" in Science-Fiction Studies 7, 1975. Reprinted in The Language of the Night, 1979.

"The Making of a Goal Machine" https://www.nytimes.com/2021/05/08/sports/soccer/bayern-munich-robert-lewandowski.html (May 8, 2021)

Iggeres HaRamban, translation by http://www.pirchei.com/specials/ramban/ramban.htm http://www.pirchei.com/specials/ramban/ramban.htm

“Trust yourself. You know more than you think you do.”