“There are two rules for success: 1.) Don’t/Never tell all/everything you know” (the joke is that the second rule is not given) is a popular saying about success that has been included in many quotation collections. “Two Rules for Success: 1. Never tell people everything you know” has been cited in print since at least February 1998.
 
“Roger H. Lincoln” has been credited for the saying since at least 1999, but it’s not known who this person is or when he said it.
 
     
Google Groups: alt.fan.don-imus
John
2/26/98
(...)
Two Rules for Success
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1. Never tell people everything you know.
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stolen from .(JavaScript must be enabled to view this email address)
   
Google News Archive
17 March 1998, Spartanburg (SC) Herald-Journal, “The Stroller” by Lou Parris, pg. B1, col. 1:
Quips a wag: “There are two rules for success in life. Rule 1: Don’t tell people everything you know.”
 
Google Books
The Ghost: A Novel
By Marc Olden
New York, NY: Simon & Schuster
1999
Pg. 131:
The Watcher said, “There are two rules for success in life, Denny. Number one: Never tell everything you know.”
 
23 August 1999, Augusta (GA) Chronicle, “Test your workplace for feds” by Bill Kirby, pg. B1, col. 1:
There are two rules for success…
1. Never tell everything you know.
—Roger H. Lincoln
 
Google Books
Business Wit & Wisdom
By Richard S. Zera
Washington, DC: Beard Books
2005
Pg. 224:
The executive reflected for a moment and responded, “There are two rules for success in any organization. Rule No. 1: Never tell people everything you know. Are there any more questions?”
—The Jokesmith
 
Blue MauMau
Great Franchise Quotes
Posted Wed, 2005/11/16 - 14:23 by Don Sniegowski
(...)
“There are two rules for success… 1) Never tell everything you know…” - Franchise owner
 
1 August 2009, Des Moines (IA) Register, “Better Twittering: Focus on the meaning, and smile” by Mike Kilen, Life, pg. 1:
This from TwitLOL.com (“Funny Tweets in Under 140 characters”): “There are two rules for success: 1.) Don’t tell all you know.”
   
The Standard (Hong Kong)
Looking for laughs? Try being cruel and abusive to yourself
Friday, March 26, 2010
(...)
5. Challenge your audience with clever lines. For example, you could use a pause as a punchline. “There are two rules for success: 1) Don’t tell all you know.” (Loooong pause).
 
14 clicks
Best 101 Entrepreneurship Quotes Ever
BY NICHOLAS TART ON MARCH 25, 2011
Success Quotes
“There are two rules for success. 1) Never tell everything you know.” Roger H. Lincoln
 
Google Books
Change Or Die—The Business Process Improvement Manual
By Maxine Attong and Terrence Met
Boca Raton, FL: CRC Press
2013
Pg. 183:
There are two rules for success: (1) Never tell everything you know.
—Roger.H..Lincoln