Questioning assumptions: One company's answer to the planner's nemesis

How familiar is the lament, “It wasn't our plans that went wrong, it was our underlying assumptions.” Each year, planners carefully integrate products, cost of goods sold, marketplace tactics, and earnings results into superbly constructed plans. Then the realization dawns that the whole structure was built on a base of false assumptions — or that major factors were completely missed. And suddenly the plans are worth less than the paper they're written on.