Source: Your Forces and How to Use Them (1912), p. 219
“The deceived has the better of the deceiver.”
Lo ingannatore rimane a pié dello ingannato.
Second Day, Ninth Story (tr. J. M. Rigg)
The Decameron (c. 1350)
Original
Lo ingannatore rimane a pié dello ingannato.
The Decameron (c. 1350)
Help us to complete the source, original and additional information
Giovanni Boccaccio 27
Italian author and poet 1313–1375Related quotes

“It is a double pleasure to deceive the deceiver.”
C'est double plaisir de tromper le trompeur.
Book II (1668), fable 15 (The Cock and the Fox).
Fables (1668–1679)
Variant: It is twice the pleasure to deceive the deceiver.

“Therefore do not deceive yourself! Of all deceivers fear most yourself!”

“It's not right to hurt or deceive someone who's already been hurt and deceived.”
Source: The Cider House Rules

“Propaganda does not deceive people; it merely helps them to deceive themselves.”
From The Passionate State of Mind, and Other Aphorisms (1955), p. 260 ; as cited in The Columbia Dictionary of Quotations https://en.wikiquote.org/wiki/Special:BookSources/0231071949, ed. Robert Andrews, Columbia University Press (1993), p. 741
The Passionate State Of Mind, and Other Aphorisms (1955)

“Men who can succeed in deceiving no one else will succeed at last in deceiving themselves.”
Miss Mackenzie, Ch. 13. (1865) · Project Gutenburg e-text http://www.gutenberg.org/etext/24000

The Tragic Sense of Life (1913), II : The Starting-Point

“Never do I deceive you, Hastings. I only permit you to deceive yourself.”
Hercule Poirot’s Early Cases (1974)
Source: The Mysterious Affair at Styles