The proper phrasing depends on how you're using it. Here are the most common and correct options:
: A rule established by Nicky's father (played by Gerald McRaney) which states that a con man must never admit to the scam, even when caught Reddit Discussion specific twists in the film's climax, or more information on the real-life con techniques used in the movie? focus movie index
Nicky meets Jess at a high-end New York restaurant where she attempts to con him by staging a scene with a fake jealous husband. Seeing through the act, Nicky advises her never to "lose focus" when unexpected situations arise. Impressed by his skill, Jess tracks him down in New Orleans, where he is running a massive operation during the Super Bowl. The proper phrasing depends on how you're using it
Could you clarify your context?