HOW DAVID GOT HIS MOTTO (He said "go ahead" before Clint Eastwood ever did) From David Crockett: The Man and the Legend, by James Atkins Shackford.

   A particular company, in which there was 'a private, an awkward, boy-like soldier' (David, of course), had become restive and even insubordinate, and the officer made known to his men that he would not remain captain of a disobediant company. He informed them that he was going to put the matter before General Jackson and ask him what to do. When the captain set out for the general's quarters, Crockett called out that he was going along to 'see what the old general says.'
   So the captain and the private called on the general, and when the cause of the visit had been carefully explained, the general broke silence with: 'Don't you make any orders on your men without maturing them, and then you execute them, no matter what it costs; and that is all I have to say' -- a witty representation of Jackson's pith and brevity.
   The two returned to the company, and when several of the uneasy ones asked David what the general had said, Crockett's briefer and pithier summary was: 'The old general told the captain to be sure he was right, and then go ahead.'"

This story was originally reported in The Life and Times of Andrew Jackson, by A.S. Coyler, who says it was related to him by General Moore. After this incident, the phrase caught on within the army, and then spread throughout the region. David went on to be known as the "Go Ahead" man, and would even sign correspondence, "Be always sure you are right, then Go Ahead."