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Why a tiny sales blip becomes a factory panic
💡 In a supply chain where each player sees only the order beneath it, small shifts in real demand get amplified into wild swings upstream — unless everyone shares the true demand signal.
In the 1990s, Procter & Gamble noticed something strange about Pampers. Babies are wonderfully predictable customers — diaper demand barely changes week to week. Yet as P&G looked upstream, the orders got wilder: store orders swung more than sales, distributor orders swung more than store orders, and orders for raw materials swung most of all. Stable demand at the bottom, chaos at the top. Stanford's Hau Lee named this the bullwhip effect — a small flick at the handle becomes a huge crack at the tip.
Why does it happen even when nobody is acting irrationally? Each link in the chain can only see the orders from the link just below it — never the real shopper. So each one adds a safety-stock buffer, reorders in batches to save on shipping, and over-orders when supply looks tight. Stack those rational habits on top of each other and the distortion compounds at every tier.
The cost is brutal: overstocked warehouses, sudden shortages, and factories lurching between overtime and idle. The classic fix is information sharing — letting the whole chain see real end-customer demand — which is exactly what Walmart's vendor-managed inventory and modern point-of-sale data feeds are built to do.
Source: Hau L. Lee et al., "The Bullwhip Effect in Supply Chains" (MIT Sloan Management Review, 1997)