“It’s what you learn after you know it all that counts” has been a favorite saying of U.S. President Harry S. Truman (1884-1972), baseball coach Earl Weaver (1930-) and basketball coach John Wooden (1910-2010).
 
The saying has been credited to the newspaper column “Abe Martin Says,” by Kin Hubbard (1868-1930), where it appeared in 1913, 1921, 1926 and 1927. The newspaper column “Office Cat by Junius” (Edgar Allan Moss of Marion, IN) used the saying in May 1922.
   
 
Wikipedia: Kin Hubbard
Frank McKinney Hubbard (born 1 September 1868 in Bellefontaine, Ohio - died: 26 December 1930 in Indianapolis, Indiana) was an American cartoonist, humorist, and journalist better known by his pen name “Kin” Hubbard.
 
He was creator of the cartoon “Abe Martin of Brown County” which ran in U.S. newspapers from 1904 until his death in 1930, and was the originator of many political quips that remain in use. North American humorist Will Rogers reportedly declared Kin to be “America’s greatest humorist.”
     
18 March 1913, Montgomery (AL) Advertiser, “Abe Martin,” pg. 12, col. 2:
There’s only one thing t’ be said agin th’ ole fashioned mother—she allowed father t’ comb his hair in th’ kitchen. It’s what we learn after we think we know it all that counts.
 
Google News Archive
21 July 1921, Spartanburg (SC) Herald, “Abe Martin Says,” pg. 5, col. 2:
It’s what we learn after we think we know it all that counts. It seems like th’ less a feler earns th’ more determined his wife is t’ wear white.
 
15 May 1922, Naugatuck (CT) Daily News, “Office Cat” by Junius, pg. 4, col. 3:
It’s what we learn after we think we know it all that counts.
 
20 January 1927, Boston (MA) Daily Globe, “Abe Martin Says” by Kin Hubbard, pg. 18:
Love laughs at locksmiths, but wait till it bumps int’  platinum-smiths. It’s what we learn after we think we know it all that counts.
       
Google Books
Genetics;
An introduction to the study of heredity
By Herbert Eugene Walter
New York, NY: Macmillan
1938
Pg. 81:
Along with the elation that comes with the acquisition of new and stimulating knowledge in any field, however, it is well to recall the sage comment of that whimsical Hoosier philosopher “Abe Martin,” who says, “It’s what we learn after we think we know it all that counts.
 
8 April 1943, Chicago (IL) Daily Tribune, “In the Wake of the News” by Arch Ward, pg. 25:
Sudden Thoughts.
It’s what learn after you know it all that counts.
—Bill Staggs.
 
Google News Archive
29 January 1945, Daily Times (Beaver and Rochester, PA), “Reports from Washington” by Helen Essary, pg. 8, col. 3:
WASHINGTON—Perhaps one of the things wrong with the world is it’s (sic) lack of interest in copy book maxims. You know the old ones “Honesty is the best policy” and “Time and tide wait for no man,” and so on.
 
The new vice president believes in maxims. His favorite maxim Truman gave to Miss Bertha Joseph, secretary to Senator George Radcliffe of Maryland. It hangs in clear type and well framed on the first wall you see as you enter Miss Joseph’s Capitol door and says: “It’s what you learn after you know it all that counts.”
 
OCLC WorldCat record
It’s what you learn after you know it all that counts
Author: Earl Weaver; Berry Stainback
Publisher: Garden City, N.Y. : Doubleday, 1982.
Edition/Format:  Book : Biography : English : 1st ed
 
Google Books
They Call Me Coach
By John Wooden with Jack Tobin
Waco, TX: Word Books
1972
Pg. 125:
It’s what you learn after you know it all that counts.
 
Google Books
The Essential Wooden:
A lifetime of lessons on leaders and leadership
By John Wooden and Steve Jamison
New York, NY: McGraw-Hill
2007
Pg. 148:
It’s What You Learn After You Know It All That Counts.