"The difference between ordinary and extraordinary…

“The difference between ordinary and extraordinary is that little extra” is a motivational saying that has been printed on posters. The saying has been cited in print since at least 1982 and is of unknown authorship.

“The difference between ordinary and extraordinary is that little extra effort” has been used frequently in sports; New York Yankees manager Dallas Green posted the saying in the clubhouse in 1989. NFL football head coach Jimmy Johnson (who coached the Dallas Cowboys from 1989 to 1993) is most often credited with the saying, but it predates his NFL coaching years.

Google Books
Smiles
By Marcia Kaplan and David Kaplan
Art by Phil Mendez
Atlanta, GA: Cheers
1982
Pg. ?:
The difference between ordinary and extraordinary is that little extra.

15 March 1987, The Orange County Register (Santa Ana, CA), “HB agent among Tarbell’s ‘best’”, pg. H10, col. 3:
The difference between ordinary and extraordinary is that putting the extra in service.

Google Books
Weathering the Storm
By Dan Clark
Latham, NY : British American Pub.
1989
Pg. 125:
He showed that the difference between ordinary and extraordinary is that little “extra.”

23 February 1989, Newsday (LongIsland, NY), “Quotations From Chairman Green ” by Marty Noble, pg. 132:
Dallas Green posted these eight inspirational messages on the walls in the Yankees’ clubhouse in time for the first full-squad workout. “They’re sayings that I’ve read over time and liked,” Green said.
(...)
“The difference between ordinary and extraordinary is that little extra effort.”

6 July 1989, The Register Star (Rockford, IL), Real Estate Marketplace, pg. 6 ad:
“The difference between ordinary and extraordinary is that little extra!”
(Century 21—ed.)

24 July 1992, Daily Herald (Chicago, IL), sec. 7, pg. 6, col. 2 ad:
THE DIFFERENCE BETWEEN ORDINARY & EXTRAORDINARY is the extra you’ll find in this 3 bedroom ranch in Summerhill.
(Starck Realtors—ed.)

Silicon India
10 Things Phenomenal People Say Every Day
Friday, 08 February 2013, 03:04 Hrs
Bangalore: Jimmy Johnson (American football coach), once said: “The difference between ordinary and extraordinary is that little extra.”