“we should deliberately build a reasonable amount of “slack” into the system. And inventory is the most obvious place for it. Clearly, the more inventory we have, the more change we can cope with and still satisfy orders. But inventory costs money to build and keep, and therefore should be controlled carefully. Ideally, inventory should be kept at the lowest-value stage, as we’ve learned before, like raw eggs kept at the breakfast factory. Also, the lower the value, the more production flexibility we obtain for a given inventory cost.”