Chain Reaction

A chain reaction is a sequence in which each step triggers the next. One event causes another, which causes another; the reaction propagates. In nuclear physics, a neutron hits a nucleus and releases more neutrons, which hit more nuclei — the reaction sustains and can grow. In chemistry, a free radical can initiate a cascade of reactions. In strategy and organisations, the same structure appears: one default triggers margin calls that trigger more defaults; one piece of content goes viral and triggers more sharing; one adoption triggers a wave of imitators. The key is that the output of step N is an input to step N+1. The reaction is self-propagating.

Chain reactions can be controlled or uncontrolled. A controlled chain reaction (e.g. a nuclear reactor) is sustained at a steady rate. An uncontrolled one (e.g. a nuclear bomb, a bank run) grows until it runs out of fuel or hits a limit. The strategic question is whether you are inside a chain reaction (and want to sustain or dampen it) or trying to start one (and want to initiate and fuel it). Viral growth, financial contagion, and technology adoption can all be modelled as chain reactions: each adoption or event increases the probability or rate of the next.

The difference between a chain reaction and a simple cascade is that in a true chain reaction, the products of the reaction feed back into the reaction — they are both output and input for the next step. That creates the possibility of exponential growth or collapse. Use the model when you see propagation that depends on each step producing the trigger for the next. Mitigation often means breaking the chain — inserting a barrier or absorbing the propagating element so the next link never fires.

Look for sequences where each event causes the next in a way that could sustain or accelerate. The tell is propagation: the reaction moves through the system, and the rate of propagation can depend on how much "fuel" (e.g. susceptible nodes, uncommitted capital) remains.

Common misapplication: Calling any sequence a "chain reaction" when the steps do not feed back. A simple cause-effect chain (A causes B causes C) is a cascade; a chain reaction requires that the output of the reaction be an input to its continuation. Second misapplication: Assuming chain reactions run forever. They run until fuel is exhausted, a barrier is hit, or a competing reaction dominates. Model the fuel and the limits.

Self-sustaining is the defining property: the products of the reaction are the triggers for more reaction. Strategy is the same — design so that each step produces the trigger for the next.