Does improving one part improve the whole?
A local improvement can make the overall result worse. A support team could shorten calls by ending them quickly, yet create more repeat calls because problems remain unresolved. A measure of one stage is useful only when its relationship with the larger goal is understood.
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Keep the full task in view
A support team is asked to reduce average call duration. One way to achieve that is to finish conversations before fully checking whether the customer's issue is resolved.
The local number improves. But repeat calls may increase, and the total time needed to solve each issue may rise.
This is local optimisation: improving one component without considering its effect on the whole system.
A better evaluation connects the stage to the final purpose. For this example, that might involve successful resolution and total effort across repeated contacts. Short calls can still be valuable when they reflect clear explanations and efficient work. The problem appears when a component's target is treated as a complete definition of success.