“Be always sure you’re right—then go ahead!” was the motto of Alamo hero David (Davy) Crockett. It appeared on the cover of his 1834 book and was widely quoted in the 19th century.
   
   
Wikipedia: Davy Crockett
Colonel David Crockett (August 17, 1786 – March 6, 1836) was a celebrated 19th-century American folk hero, frontiersman, soldier and politician; usually referred to as Davy Crockett and by the popular title “King of the Wild Frontier”. He represented Tennessee in the U.S. House of Representatives, served in the Texas Revolution, and died at the age of 49 at the Battle of the Alamo. 
 
Google Books
A Narrative of the Life of David Crockett, of the State of Tennessee
written by himself
Philadelphia: E. L. Cary and A. Hart
1834
Cover Page:
I leave this rule for others when I’m dead,
Be always sure you’re right—THEN GO AHEAD!
THE AUTHOR.