The term "trigger" refers to a lever on brass instruments that controls a slide or valve, changing the instrument's pitch. However, authors have examined the concept both metaphorically and literally, considering its role in initiating action or response. Walter Bradford Cannon described the lethal accuracy of a trigger in warfare, while Sun Tzu compared energy to a crossbow's tension and decision to the release of a trigger.
Psychologists like William James viewed triggers as devices that initiate involuntary reactions, and writers such as Mark Twain evoked tension through "hair-trigger" states. These diverse perspectives highlight how the idea of a trigger—whether mechanical, psychological, or symbolic—functions as a catalyst for change, ranging from physical movement to emotional disturbance.