"Don’t practice until you get it right; practice until you can’t get it wrong” (or “Amateurs practice until they can get it right; professionals practice until they can’t get it wrong") is an adage popular in sports, music and business. “Amateurs practice something until they get it right. Professionals practice something until they can’t get it wrong” has been cited in print since at least 2000, when it was said to have been on a poster (probably seen at music schools).

English pianist and composer Harold Craxton (1885-1971) has been credited with the saying by quotations researcher Nigel Rees (see the 2000 citation below), but documentation is needed.


Google Books
Making Music at the Piano:
Learning Strategies for Adult Students
By Barbara English Maris
New York, NY: Oxford University Press
2000
Pg. 114:
Have you ever seen the poster that declares: “Amateurs practice something until they get it right. Professionals practice something until they can’t get it wrong”?

Google Books
Get a Grip!
Edited by John M. Capozzi
Fairfield, CT: JMC Pub. Services
2001
Pg. 141:
In golf, amateurs practice until they can get it right .. professionals practice until they can’t get it wrong.

Google Books
Mark My Words:
Great quotations and the stories behind them
By Nigel Rees
New York, NY: Barnes & Noble, Inc.
2002, ©1997
Pg. 14:
There have been several other attempts to define the difference between amateurs and professionals, beyond the acting profession: ‘Amateurs [musicians] practice until they can get it right; professionals practice until they can’t get it wrong’ (quoted by Harold Craxton, one-time professor at the Royal Academy of Music); ...

trumpetherald.com
jkramb19
Posted: Sun Aug 04, 2002 3:16 pm
(...)
Don’t practice until you get it right, practice until you can’t get it wrong.

3 November 2006, Tallahassee (FL) Democrat, “FSY layers on character for ‘Falstaff’” by Mark Hinson, pg. D22:
“He said, ‘An amateur will practice till they get it right, but professionals practice until they can’t get it wrong.’ I rather liked that.”

Hartford (CT) Business
October 1, 2007 | last updated May 26, 2012 1:31 am
Hire A Pro, It’s The Way To Go
Harvey Mackay
(...)
Mackay’s Moral: Amateurs practice until they get it right. Professionals practice until they can’t get it wrong.

7 February 2007, Daytona Beach (FL) News-Journal, “Speaker offers life tips from golf course” by Aaron London, pg. 1A:
“Good players practice until they get it right,” he said. “Great players practice until they can’t get it wrong.”
(Golf Channel lead announcer Brian Hammons—ed.)

Music-News.com
Selah
“Performing is what I want to spend my life doing”
added: 31 Jul 2010
interviewed by: Dani Valls Halling
(...)
What’s the best piece of advice you have received?
Good artists practice until they get it right, but great artists practice until they can’t get it wrong.

Google Books
The Mackay MBA of Selling in the Real World
By Harvey Mackay
New York, NY: Penguin Books
2011
Pg. ?:
Amateurs practice until they get it right. Professionals practice until they can’t get it wrong.

Philosiblog
Posted on 29 May 2012
Don’t practice until you get it right. Practice until you can’t get it wrong. – Unknown
What does that mean?
While this may not be a “real” quote, spoken by a single famous person, it is derived from a similar saying in nearly every culture from ancient times to the present. Whether it’s “Practice makes perfect” or “Tomorrow’s battle is won in today’s practice,” the notion that practice is important seems a universal concept.