“When/If your outgo exceeds your income (then) your upkeep is your downfall” is a common sense phrase for a person to live within his or her means. The phrase is cited in print from at least 1945 and is said to have been printed on a World War II poster.
 
   
20 May 1945, Paris (TX) News, pg. 3, col. 8:
When your outgo exceeds your income your upkeep is your downfall.
 
Google News Archive
10 January 1954, Sarasota (FL) Herald-Tribune, “Earl Wilson’s Broadway,” pg. 6, col. 4:
WISH I’D SAID THAT: Sherry Britton recalls this truism: “When your outgo exceeds your income, your upkeep is your downfall.”
   
21 May 1956, Los Angeles (CA) Times, “Cityside with Gene Sherman,” pg. 2:
If your outgo exceeds your income, then your upkeep will be your downfall.
   
Google Books
Apples of Gold
By Jo Petty
Norwalk, CT: C.R. Gibson
1962
Pg. 85:
“If your outgo exceeds your income, then your upkeep will be your downfall.”
 
8 July 1966, Wall Street Journal, “PEPPER…and Salt”:
“Ladies and gentlemen, what our speaker has been telling you is that if your outgo exceeds your income, then your upkeep will be your downfall.”
     
Google News Archive
11 August 1966, Sarasota (FL) Herald-Tribune, “It Happened Last Night” by Earl Wilson, pg. 34, col. 4:
Remembered Quote: Bill Earle explains economy very simply in Quote: “If your outgo exceeds your income, then your upkeep will be your downfall.”
 
Google Books
The Educator’s Book of Quotes
By John Blaydes
Thousand Oaks, CA: Corwin Press,
2003
Pg. 100:
“If your outgo exceeds your income, then your upkeep will be your downfall.”
—World War II Poster