Ohno considered the fundamental waste to be overproduction, since it causes most of the other wastes. Producing more than the customer wants by any operation in the manufacturing process necessarily leads to a build-up of inventory somewhere downstream: the material is just sitting around waiting to be processed in the next operation. Mass or larger-batch manufacturers might ask, "What's the problem with this, as long as people and equipment are producing parts?" The problem is that big buffers (inventory between processes) lead to other suboptimal behavior, like reducing your motivation to
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