Paul Arden (1940-2008), a former creative director for the advertising firm Saatchi & Saatchi, popularized a phrase with the title of his book, It’s Not How Good You Are, It’s How Good You Want To Be (2002). A person can become better if he or she has the motivation and gives the effort.
 
Similar phrases were cited earlier than Arden’s book. “It’s simply a case of ‘how good do you want to be?’” was cited in print in 1951. “You’ve got to make up your mind how good you want to be, and then work at it” was cited in print in 1965. “How good you become depends largely upon how good you want to be” was cited in print in 1967.
   
 
Wikipedia: Paul Arden
Paul Arden (7 April 1940 – 2 April 2008) was an influential author of several books on advertising and motivation including “Whatever You Think, Think The Opposite” and “It’s Not How Good You Are, It’s How Good You Want To Be” and a former creative director for Saatchi and Saatchi at the height of their advertising might.
 
7 August 1951, The Evening Independent (Massillon, OH), “The Bull Pen” by Bob Dixon, pg. 11, col. 1:
By fall he hopes to have his squad tentatively selected and get right down to the serious work ahead.
 
“It’s simply a case of ‘how good do you want to be?’ Nobody wants to play 1920-brand football.”
(Chuck Mather—ed.)
 
7 February 1965, The Oregonian (Portland, OR), “Bowling Clinic” by Billy Sixty,
When I was a kid my teacher, Jimmy Smith, match king for 15 years (1907-1922), used to say: “You’ve got to make up your mind how good you want to be, and then work at it.”
 
Google Books
Bud Wilkinson’s Guide to Modern Physical Fitness
By Bud Wilkinson
New York, NY: Viking Press
1967
Pg. 142:
How good you become depends largely upon how good you want to be.
 
OCLC WorldCat record
It’s not how good you are, it’s how good you want to be
Author: Paul Arden
Publisher: London ; New York : Phaidon, 2003.
Edition/Format:   Book : English
Summary:
“It’s Not How Good You Are… is a concise guide to making the most of yourself—a pocket ‘bible’ for the talented and timid to make the unthinkable thinkable and the impossible possible. After decades at the top of one of the world’s most competitive industries, Paul Arden offers insights into such diverse subjects as the value of being fired and why it’s often better to be wrong than to be right. He gives original and logical answers to everyday questions. Much of it appears obvious when you read it, but aren’t all questions easy when you know the answers? Whether you are a school-leaver, self-employed or a managing director, this book is invaluable for everyone who aspires to succeed. Book jacket.”—BOOK JACKET.
 
29 September 2003, USA Today, “Tiny book is packed with career inspiration” by Bruce Rosenstein, pg. B10:
What you’ll discover: [Paul Arden] favors short paragraphs. In big type. In wildly different styles of typography. With lots of arresting photographs and sketches. With some pages containing only a word or two. Not unlike an ad, come to think of it.
 
Arden made his mark in a long advertising career, including 15 years as executive creative director of Saatchi & Saatchi. Roger Kennedy, the book’s designer, was head of typography there for 20 years.
 
Arden offers short, pithy advice to people working in advertising agencies, but applicable to anyone striving for excellence.