the.com/chain reaction

means A self-sustaining sequence where each event triggers the next in line, so one small push ends up causing a whole cascade.

from Born in nuclear physics in the early 20th century, describing how a split atom flings out neutrons that split more atoms, which fling out more neutrons, and so on — the term itself borrowed the everyday image of a literal chain, each link pulling the next. It leapt into common speech especially after the physics became world-famous (atomic power, atomic weapons), and 'chain reaction' came to describe any domino-like unraveling, from gossip to riots to a bad day.