"How come anything you buy will go on sale next week?” is a jocular saying that has been printed on many images. American humorist Erma Bombeck (1927-1996) asked the question in her syndicated newspaper column on April 2, 1987.


Wikipedia: Erma Bombeck
Erma Louise Bombeck (née Fiste; February 21, 1927 – April 22, 1996) was an American humorist who achieved great popularity for her newspaper column that described suburban home life from the mid-1960s until the late 1990s. Bombeck also published 15 books, most of which became bestsellers. From 1965 to 1996, Erma Bombeck wrote over 4,000 newspaper columns, using broad and sometimes eloquent humor, chronicling the ordinary life of a midwestern suburban housewife. By the 1970s, her columns were read twice-weekly by 30 million readers of the 900 newspapers in the U.S. and Canada.

2 April 1987, The Republic (Columbus, IN), “Trivia facts often keep people up at night” by Erma Bombeck, pg. B4, col. 3:
“How come anything you buy will go on sale next week?”

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FW: When God Created Mothers
R.Cody
5/15/07
(...)
Quotes from Erma Bombeck
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How come anything you buy will go on sale next week?

Twitter
Solaria
@solphoto
Erma Bombeck “How come anything you buy will go on sale next week?” (Canon’s Lenses went on discount 7 days after I purchased my 70-200)Grrr
3:01 PM - 7 May 2009

Google Books
Women and Comedy:
History, Theory, Practice
Edited by Peter Dickinson, Anne Higgins, Paul Matthew St. Pierre, Diana Solomon and Sean Zwagerman
Lanham, MD: Rowman & Littlefield
2013
Pg. XXVII:
Erma Bombeck’s many jokes about the plight of the housewife— “How come anything you buy will go on sale next week?”; ...

Twitter
Carl Hult
@Carlswall
How come anything you buy will go on sale next week?
- Erma Bombeck again
3:22 PM - 17 Apr 2019