“The sun don’t shine on the same dog’s butt every day” (investment proverb)

“The sun doesn’t/don’t shine on the same dog’s ass/back/butt/eyes/tail every day/all the time/forever” means that one can’t expect to get lucky and have some nice sunshine every single day. The saying has been cited in print since at least 1927 and appears to come from the South.
 
The saying has been popular with baseball players. New York Yankee baseball greats Mickey Mantle (from Oklahoma) and Catfish Hunter (from North Carolina) both used the saying. In finance, the saying means the same as “into each life. some rain must fall” or “you can’t win them all.”
 
 
American Proverbs and Folksayings about Animals and Birds
The sun doesn’t shine on the same dog’s back everyday.
     
Wikipedia: Babe McCarthy 
James Harrison “Babe” McCarthy, sometimes called “Ol’ Magnolia Mouth” or just “Magnolia Mouth”, was an American professional and collegiate basketball coach. McCarthy was originally from Baldwyn, Mississippi. McCarthy may best be remembered for Mississippi State’s appearance in the 1963 NCAA Men’s Division I Basketball Tournament when his all-white team sneaked out of town in order to face Loyola University Chicago, which had four black starters.
 
In March 1975, McCarthy died as a result of colon cancer.
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Babe-isms
Babe-isms were short funny phrases that earned McCarthy his nickname. A few of the more famous (and often used) Babe-isms were:
“My old pappy used to tell me the sun don’t shine on the same dog’s butt every day.”
 
Wikiquote: Damages (TV series)
Damages (2007-) is an American legal drama, airing on FX, about the world of New York City high-stakes litigation. The series, which provides a view into the true nature of power and success, follows the turbulent lives of Patty Hewes, the nation’s most revered and reviled high-stakes litigator, and her bright, ambitious protégé Ellen Parsons.
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Season One
A Regular Earl Anthony [1.05]

Ray: I’m worried the sun don’t shine on the same dog’s tail all week.
Arthur: I have no idea what that means.
Ray: It means we got lucky.
   
Google Books
The Typographical Journal
Volume 71
1927
Pg. 544:
Msop — or some old sop — once said: “The sun doesn’t shine on the same dog all the time.”
         
Google News Archive
12 March 1938, Deseret News (Salt Lake City, UT), “Nowak Case Makes Indians Look Funny” by Gale Talbot, Sports, pg. 3, col. 3:
“Sure,” says Oscar Vitt, the Indians’ new manager. “We forgot to promulgate Nowak’s contract. But that’s no excuse for Terry to be quite so sharp about it. As I always say: The sun doesn’t shine forever on the same dog, and something’s going to happen to Terry if he keeps this up.”
 
4 August 1940, Cleveland (OH) Plain Dealer, “Indians’ 4 runs in 1st chase Gomez” by Gordon Cobbledick, pg. C1, col. 7:
The last time the two veteran southpaws tangled was in New York a few weeks ago and Smith was kayoed by a seven-run attack in the first inning, proving that the sun doesn’t shine in the same dog’s eyes all the time.
 
Google Books
The Dissenters
By Sigurd Jay Simonsen
New York, NY: Fortuny’s Publishers, Inc.
1941
Pg. 198:
“Times change and as I’ve said before, the sun doesn’t shine on the same dog all the time.”
 
Google Books
One on the House
By Mary Lasswell
Boston, MA: Houghton Mifflin
1949
Pg. 58:
“Hel!, the sun don’t shine on the same dog’s butt all the time! Let’s have that beer . . . our luck’s bound to change in the second.”
 
Google Books
26 April 1954, Life magazine, pg. 64, col. 3:
Snead, putting steadily, shot a subpar 70, one better than Hogan, won nearly $10000, remarked in his best West Virginia manner, “The sun don’t shine on the same dog’s tail all the time.”
     
OCLC WorldCat record
The farmer
Author: Porter Wagoner
Publisher: New York : RCA Victor, 1973.
Edition/Format:  Music LP : Country music : English
Contents:
Conversation—
The farmer—
Daddy’s working boots—
My dad—
Moments of meditation—
Wake up, Jacob—
The county farm—
The sun don’t shine (on the same dog every day)—
 
Google Books
November 1976, Texas Monthly, ‘Orange Peril” by Gary Cartwright, pg. 124, col. 3:
What DKR (University of Texas football coach Darrell K. Royal—ed.) really talks about is red beans and how ol’ ugly is better than ol’ nothing and why the sun don’t shine on the same ol’ dog’s ass every day and how when the big scorekeeper finally comes to write against your name all he really wants to know is who won.
   
The Internet Movie Database
Memorable quotes for
Hoosiers (1986)

Opal Fleener: Sun don’t shine on the same dog’s ass everyday, but, mister you ain’t seen a ray of light since you got here.
 
Google Books
All My Octobers:
My Memories of Twelve World Series When the Yankees Ruled Baseball

By Mickey Mantle with Mickey Herskowitz
New York, NY: Harper
2006, ©1994
Pg. 100:
But as we say in Oklahoma, the sun don’t shine on the same dog’s ass every day.
 
Google Books
When You Come to a Fork in the Road, Take It!:
Inspiration and Wisdom from One of Baseball’s Greatest Heroes

By Yogi Berra with Dave Kaplan
New York, NY: Hyperion
2002, ©2001
Pg. 18:
As Catfish Hunter used to say, “The sun don’t shine on the same dog’s ass all the time.”
 
Google Books
The First Time Investor:
How to Start Safe, Invest Smart, and Sleep Well

By Larry Chambers and Dale Rogers
New York, NY: McGraw-Hill
2004
Pg. 55:
The sun does not shine on the same dog’s tail every day.
 
Google Books
Empire City:
New York Through the Centuries

By Kenneth T. Jackson and David S. Dunbar
New York, NY: Columbia University Press
2005
Pg. 788:
The Yankees have seen frustration as well as success. As their great 1970s pitcher Catfish Hunter once remarked after losing a game, “the sun don’t shine on the same dog’s ass every day.”
 
Alkaline Earth
July 17, 2007
Since moving to Texas, I’ve heard many variants of the following expression:
I: “The sun don’t shine on the same dog’s ass all the time.” (attr. Catfish Hunter, Darrel Royal)
“Sun don’t shine on the same dog’s ass everyday, but, mister you ain’t seen a ray of light since you got here.” (Hoosiers)
II: “The sun’s got to shine on a dog’s ass some time. (And the sun’s gonna shine in my backdoor someday.)” (on web)
III: “The sun even shines on a dog’s ass some days. Anybody can win the lottery. Know what I’m saying?” (White Men Can’t Jump)