This is a case study from a Japanese leading cosmetics company.
The company received a complaint that a consumer had bought a soap box that was empty. Immediately the authorities isolated the problem to the assembly line, which transported all the packaged boxes of soap to the delivery department. For some reason, one soap box went through the assembly line empty. Management asked its engineers to solve the problem. Post-haste, the engineers worked hard to devise an X-ray machine with high- resolution monitors manned by two people to watch all the soap boxes that passed through the line to make sure they were not empty. It was effective but came at a huge cost.
The same problem was also posed to workers on the assembly line. One came up with this cost-effective solution:
He placed a heavy-duty industrial electric fan near the exit-point of the conveyor belt, switched on the fan, and while filled soap boxes passed the fan, empty boxes were blown off the line.