The idiom "一发不可收拾" is formed by combining "一发" (literally "one shot", indicating a single trigger) with "不可收拾" (literally "cannot tidy up", meaning uncontrollable), where each character contributes to a conditional cause-and-effect structure: 一 (one) and 发 (to shoot) set up an initial action, while 不 (not), 可 (can), and 收拾 (to control or tidy) negate the possibility of containment, resulting in a phrase that describes a situation spiraling out of control after a starting point.