Reduce the number of defective products

According to TOYOTA's solution to the problem:

"Based on experience and intuition alone, it is impossible to address the root of the problem. Thinking through the problem-solving process is extremely necessary.

So how to clarify the problem?

Toyota has said that when choosing the problem, it is necessary to clarify the reason for starting to solve this problem. The basis for this selection is "Metric"

Source: Solve problems in TOYOTA mode