“One book that always has a sad/unhappy ending is a check book” is a jocular one-line saying that compares a check book (or “checkbook”) to a book of fiction. The saying has been cited in print since at least 1939 and 1942 and is of unknown authorship.
 
     
Google Books
June 1939, Boys’ Life, “Think and Grin” edited by Frank Rigney, pg. 33, col. 4:
Too Much Drawing
Well, my book had a sad ending.
Your book?
Yes, my “check book.”
   
Google Books
The Balance Sheet
Volume 24
1942
Pg. 380:
One book that always has a sad ending is a check book.
 
4 November 1942, Edwardsville (IL) Intelligencer, pg. 4, col. 3:
One book that always has a sad ending is a check book.
 
Google News Archive
14 December 1955, Portsmouth (OH) Times, “Pete’s Pungent Patter” by Pete Minego, pg. 25, col. 3:
There is a book that always has a sad ending — your check book.
 
10 July 1961, Chicago (IL) Tribune, “Front Views & Profiles” by Kay Loring, pg. B7:
Emcee Jack Herbert’s observation that one book which usually has an unhappy ending is a check book.
 
15 March 1971, Lubbock (TX) Avalanche-Journal, “The Plainsman,” pg. A-8, col. 1:
The book with the unhappiest ending usually is a family checkbook.
 
Google Books
14,000 Quips and Quotes for Speakers, Writers, Editors, Preachers, and Teachers
By E. C. McKenzie
Grand Rapids, MI: Baker Book House
1990, ©1980
Pg. 48:
The one book that always has a sad ending is a checkbook.
   
Google Books
1000 Stories and Illustrations for All Occasions
By Herbert V. Prochnow
Grand Rapids, MI: Baker Books
1994, ©1972
Pg. 24:
The one book that always has a sad ending is the check book.
 
Google Books
A Compact Guide to Balancing Your Life
By Brad Lewis
Colorado Springs, CO: NavPress
2001
Pg. 148:
The one book that always has a sad ending is a checkbook.