A piece of homespun philosophy often used ironically, the U.S. phrase a man’s gotta do what a man’s gotta do, and variants, mean that a man must do what he feels needs to be done, even if it is dangerous or undesirable.
These are the earliest occurrences of the phrase that I have found, in chronological order:
1-: From The Grapes of Wrath (New York: The Viking Press, 1939), by the U.S. novelist John Steinbeck (1902-1968):
Casy said quickly, “I know this—a man got to do what he got to do.”
Pa took the dirty bill and gave Uncle John two silver dollars. “There ya are,” he said. “A fella got to do what he got to do.”
2-: From the review of Steinbeck’s The Grapes of Wrath by Arthur D. Spearman *, published in the San Francisco Examiner (San Francisco, California) of Sunday 4th June 1939—bold type is the author’s own emphasis:
The objectives of the writer are revealed in the reflective psychoses of the ex-Preacher Casy who is the principal vehicle for Steinbeck’s radical and deracinate propaganda […].
As Steinbeck himself might phrase it from the lips of his sage, ex-Preacher Casy, “A man just gotta do what he gotta do,” and in Steinbeck’s code, that goes for fornication, rape, murder, going on a drunk, or whatever a man has an urge to do. A propagandist just “gotta do what he gotta do.” Otherwise he could never satisfy his ambition, or the plotting of his friends.
(* Arthur D. Spearman, of the Society of Jesus, was the director of the library of Loyola University, Los Angeles; he was the son of the U.S. novelist Frank H. Spearman (1859-1937).)
3-: From The Tragedy of Eldorado, the review of Steinbeck’s The Grapes of Wrath by the British-born U.S. novelist Christopher Isherwood (1904-1986), published in The Kenyon Review (Gambier, Ohio: Kenyon College), Vol. 1, No. 4, Autumn, 1939—Isherwood mentioned:
the ex-preacher Casy, a neo-Tolstoyan figure, agnostic and perplexed, whose provisional creed is: “You gotta do what you gotta do.”
4-: From Students Are Paying For Professors’ Sins, by Robert L. Riggs, published in The Courier-Journal (Louisville, Kentucky) of Thursday 11th July 1940:
[I have no] doubt that the people now in college will perform their duty toward their nation, in peace or war. A man has got to do what he’s got to do, and today’s undergraduates, I believe, will rise to whatever the occasion requires of them.
5-: From “A Pledge For Today”, by Private First Class William A. Shewbart, published in the Franklin County Times (Russellville, Alabama) of Thursday 5th November 1942:
Men call it V! They call it a vow for Victory. Victory over Nazism. Yeah, that must be right I guess. But never mind what its [sic] called, this fight. You know, a guy’s gotta do what he’s gotta do.
6-: From the column Of Many Things, by Thomas E. Murphy, published in The Hartford Courant (Hartford, Connecticut) of Wednesday 17th December 1952—the author writes that he recently noticed, in front of the od State House, “the dirtiest, sauciest, fattest street urchin of a sparrow” who “didn’t live off the crumbs from the pigeons [but took them] right out of the pigeons’ mouths”:
He is probably thanking his sparrow stars that one day he discovered how dumb pigeons really are. It was on that day that he decided to quit the sparrow gang and run with the pigeons. “I’m sorry, Maw, but nobody never feeds no sparrows. But everybody’s always throwing goodies to the pigeons.”
“Son, if you must, you must. A man’s got to do what he’s got to do. And if the gay lights downtown and the mad whirl of pigeon life is what you wants, then I say, Son, go to it with my blessing.”
The phrase has been associated with the U.S. actor John Wayne (Marion Michael Morrison – 1907-1979)—for example by Clarence Petersen, on two occasions, in the Chicago Daily Tribune (Chicago, Illinois):
1-: In Scripts’ Success Spelled C-l-i-c-h-e, published on Sunday 14th February 1960:
If you have the ability to listen carefully and write down all you hear, you ought to be able to turn many an evening’s late TV movie watching into a profitable career as a screen writer.
There’s hardly any trick to it. You simply wait for one of the channels to schedule a John Wayne movie. When it comes on—and you’ll not wait long—get out half a dozen pencils and a ream of paper and jot down the cliches.
Later, rearrange your notes into a new sequence, send the product off to Hollywood, and wait for the royalties.
They’re almost sure to come because you’ll have done what Wayne’s professional writers seem to have been doing with great success for more than a decade.
A must for any Wayne script, it would seem, is the line, “A man’s gotta do what he’s gotta do.” For variation you can do what the pros once had to do, put the words into the heroine’s mouth, “A man needs a woman to give him what she’s got to give so he can do what he’s gotta do.” [Despite this eloquent plea, incidentally, Wayne went off without her.]
2-: In the review of The Four Days of Naples (Le quattro giornate di Napoli – 1962), an Italian film directed by Nanni Loy—review published on Monday 13th May 1963:
The power of the film is unfettered by the war movie cliches audiences have come to expect. There are no Jon Waynes to announce before an act of courage that “a man’s gotta do what he’s gotta do.” In “Four Days,” they just go ahead and do it. It is one of the best films of World War II.
According to Roz Warren in Women’s Lip: Outrageous, Irreverent and Just Plain Hilarious Quotes (Naperville, Illinois: Hysteria Publications, 1998), the U.S. comedienne Rhonda Hansome coined the following anti-proverb:
A man’s got to do what a man’s got to do. A woman must do what he can’t.