whatA supply chain of four stages: shop, wholesaler, distributor, factory, drawn as four stacked order traces with the factory on top. Customers buy with a five percent whisper of randomness around a steady hundred. Each stage sees only the orders from the stage below, smooths them into a forecast, holds a safety stock, and orders upstream to cover forecast plus whatever inventory has drifted. Deliveries take three and a half seconds.

whyThe claim: the whisper becomes a whip. Every stage's corrections ride the corrections below, lagged by the lead time, so amplitude grows at each step upstream: the calm retail line widens to factory whiplash of forty percent and more, feast and famine born of prudent bookkeeping. Nobody panics; everybody smooths; the whip comes anyway. Click to share the shop's true demand with every stage and it flattens to a fraction while you watch.

howThe beer game in continuous time: exponential-smoothing forecasts, order-up-to targets covering lead time plus safety stock, backorders allowed, orders clipped at zero. The swing figures in the corner are coefficients of variation over the last minute. Left alone the chain cycles between hoarding-by-rumour and shared truth every fifty-five seconds. One integer seeds the customers, so the same seed sells the same coffee.