quick on the trigger

quick on the draw

1. Literally, very quick at drawing one's gun in readiness to shoot it. The gunfighter was so quick on the draw that he often shot his enemies before they reached their own gun.
2. By extension, understanding, anticipating, or reacting to a given situation or circumstance very quickly. You have to be quick on the draw if you want to get ahead in the world of business. Faced with criticism by environmentalists, the company's PR rep was quick on the draw and pointed out its important role in job creation for the local community. John is quick on the draw to defend himself when criticized.
See also: draw, on, quick

quick on the trigger

 and quick on the draw 
1. Lit. quick to draw a gun and shoot. Some of the old cowboys were known to be quick on the trigger. Wyatt Earp was particularly quick on the draw.
2. Fig. quick to respond to anything. John gets the right answer before anyone else. He's really quick on the trigger. Sally will probably win the quiz game. She's really quick on the draw.
See also: on, quick, trigger
References in classic literature ?
Always a child," said Gobseck to Gigonnet, "you are too quick on the trigger.