“Everybody/Everyone has two businesses—his own and show business” is one of the oldest entertainment sayings. “Thoughtless souls who mouth the old wheeze that everyone has two businesses” was cited in print in 1937. Clifton Fadiman’s The American Treasury, 1455-1955 (1955) credited the saying to actress Judith Anderson (1897-1992), but there’s no documentary evidence to give Anderson any special credit for the popular saying.
 
The saying means that everyone has his or her own business, but everyone also insists to know something about show business. In 1953, it was stated that this has been “said around the Lamb’s and Lindy’s and Sardi’s (New York City institutions for actors—ed.) virtually forever.”
 
 
8 July 1937, Kerrville (TX) Mountain Sun, pg. 6, col. 2:
Dallas News: Thoughtless souls who mouth the old wheeze that everyone has two businesses, his own and show business, overlook an even more widespread observation. This is the belief, endemic at least in Texas, that no one outside an institution for the feeble-minded is disqualified as an art critic.
 
2 March 1947, New York (NY) Times, “Mr. Hopkins Looks at the Theatre” by Arthur Hopkins, pg. SM18:
It was once said that every man knows two businesses, his own and show business.
 
Google News Archive
9 August 1947, Ottawa (Ontario) Citizen, “Eddie Cantor’s Tales About Show Business” by Eddie Cantor, pg. 21, col. 6:
‘There’s no business like show business”—so goes the song written by Irving Berlin in the Broadway musical smash, “Annie Get Your Gun.”
 
Every person I have ever met has two businesses— his and show business. I’ve had the boy who delivers the groceries to my house in Beverley Hills say, “Heard your show last night, Eddie…a little off on the timing, weren’t you?” You see what I mean?
 
4 October 1953, San Diego (CA) Union, “Real showmen urged as aid to expanding TV” by Jack O’Brian, pg. E-7, col. 7:
As they have said around the Lamb’s and Lindy’s and Sardi’s virtually forever:
 
“Everyone has two businesses—his own and show business.”
 
18 November 1953, The Times-Picayune (New Orleans, LA), “Looking at Hollywood” by Hedda Hopper, pg. 45, col. 4:
It’s said that all people have two businesses—their own and show business. I’m beginning to believe that’s true.
 
13 December 1953, Dallas (TX) Morning News, “The Passing Show” by Jack Rosenfield, pt. 7, pg. 1, col. 1:
You Have Two Businesses
“Everybody has two businesses, his own and show business,” moans the showman just after he has been given some well-meant but hardly helpful advice by a paying customer from the collars and ties line.
     
Google Books
The American Treasury, 1455-1955
By Clifton Fadiman
New York, NY: Harper
1955
Pg. 834:
Everybody has two businesses — his own, and show business.
JUDITH ANDERSON
 
The Wall Street Journal
OPINION
March 9, 2006
Boy in a Bubble
What George Clooney doesn’t know about life.
By Peggy Noonan
(...)
Which, of course, you know. In the days after Oscar, the one old saying everyone in Hollywood keeps remembering over and over is, “Everyone has two businesses, his own and show business.”
 
New York (NY) Times
Rock Stars for a Night, and for a Price
By LARRY ROHTER
Published: January 18, 2011
(...) 
“Everybody has two businesses, their own business and show business,” Mr. Fishof, 54, said.
 
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Everybody has two businesses, their own business and show business… http://fb.me/JYUMcSGv
11:49 AM - 20 Jan 11
 
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‘Everybody has two businesses, his own business and show business.’ Daily Variety axes print edition: http://n.pr/Xv3h72
7:46 AM - 22 Mar 13