Don’t bring a knife to a gunfight

A modern American idiom that has come to mean, be adequately prepared or equipped for any confrontational situation. The origin is the movie The Untouchables (1987) where Malone, the Sean Connery character, wielding a sawn-off shotgun, exclaims, “Isn't that just like a wop! Brings a knife to a gunfight!” Then chases his knife-wielding adversary down the stairs. The same words, or similar, have been used in over twenty movies since. The Untouchables was based on the book of the same name written by Oscar Fraley in 1957, but the idiom does not appear in the book. The authorship, therefore, must go David Mamet, who wrote the screenplay for the movie, but may have heard the expression before he included it in his screenplay. Some say it's an old Texas expression, but no citation before 1987 has ever been found.