The "Bullwhip Effect," a concept developed in the 1990s by Procter & Gamble and Dr. Hau Lee of Stanford, is one of the most important basic concepts in supply chain.
The Bullwhip Effect, in great summary, means that as you go further back up stream in the supply chain, and away from actual customer demand, information signals about that demand are delayed and distorted. So, for example, while actual consumer pull in retail may be relatively stable, demand, usually in the form of orders, starts to swing more widely to direct retail suppliers and even more so to the suppliers' suppliers.