Numbers are an indicator that the manager should act.

Tired: ”You didn’t meet your KPIs. You shall be penalised.”
Wired: ”You didn’t meet your KPIs. Why not and what do you need?”

By all means have KPIs and other metrics but don’t manage by them. use them only as indicators, it’s in the name.

You can’t use numbers to judge humans. The explanation is always too complex. Numbers are dehumanising.

A weed is just a plant in the wrong place. As a people manager, it’s your job to help employees find the right place. Occasionally that place is outside the organisation, but usually not. If someone is failing to perform that reflects as much on their manager as themselves. A manager’s job is to work with what they’ve got.

Numbers tell you when agiltiy is needed: change what you’re doing.