In redesigning the switch assembly example, what was the initial practical problem Shingo addressed?

Answer

Workers frequently forgot to insert a necessary spring

Shingo addressed the problem where workers frequently forgot to insert a necessary spring under one of the buttons by redesigning the task into distinct steps involving a placeholder for immediate detection.

In redesigning the switch assembly example, what was the initial practical problem Shingo addressed?
inventorManufacturingqualityprincipleerror proofing