“The hardest tumble a man can take is to fall over his own bluff.”

Source: Duma Key

Josh Billings: His Works, Complete (1873)

Of Revenge
Essays (1625)
Variant: Certainly, in taking revenge, a man is but even with his enemy; but in passing it over, he is superior; for it is a prince's part to pardon.

Source: The Stars My Destination (1956), Chapter 14 (p. 221).

An earlier unattributed version of this quip appeared in What Man Can Make of Man (1942) by William Ernest Hocking: "He lends himself to the gibe that he is 'so very liberal, that he cannot bring himself to take his own side in a quarrel.'" http://www.barrypopik.com/index.php/new_york_city/entry/a_liberal_is_a_man_too_broad_minded_to_take_his_own_side_in_a_quarrel/
Source: As quoted by Guy Davenport (The Geography of the Imagination) at page x in A Liberal Education http://books.google.de/books?id=Dly0RgUc0YcC&pg=PR10&dq=A+liberal+is+a+man+too+broadminded+to+take+his+own+side+in+a+quarrel.&hl=de&sa=X&ei=Xt_OUZSGJcjLswaApYDQBg&redir_esc=y#v=onepage&q=A%20liberal%20is%20a%20man%20too%20broadminded%20to%20take%20his%20own%20side%20in%20a%20quarrel.&f=false by Abbott Gleason (Cambridge, Massachusetts, USA, Tide Pool Press, 2010).
Source: As quoted by Harvey Shapiro “Story of the Poem”, 15 January 1961, New York (NY) Times, Section SM page 6 https://www.nytimes.com/1961/01/15/archives/story-of-the-poem-the-story-of-the-poem.html?searchResultPosition=1

Rouben Mamoulian in Lecture and discussion at University of Southern California, December 7, 1975. Tape recording, Special Collections, University of Southern California. (M).

World Wildlife Fund: British National Appeal Banquet, London (1962)
The Environmental Revolution: Speeches on Conservation, 1962–77 (1978)
Context: For conservation to be successful it is necessary to take into consideration that it is a characteristic of man that he can only be relied upon to do anything consistently which is in his own interest. He may have occasional fits of conscience and moral rectitude but otherwise his actions are governed by self-interest. It follows then that whatever the moral reasons for conservation it will only be achieved by the inducement of profit or pleasure.

"Psychological Observations"
Parerga and Paralipomena (1851), Studies in Pessimism
Variant: Everyone takes the limits of his own vision for the limits of the world.
Source: Studies in Pessimism: The Essays