graph a and b

All processes have variation. You can never predict exactly what will happen but you can predict broad behaviour patterns.

Which is more predictive, A or B?

B is more predictable. If a manager acts on any data point in either chart, he or she could increase variation. The only way to reduce variation is to act on the process or system.

Responding to a data point is paying attention to output.

Seeking to understand the causes of variation and acting on them is paying attention to process.