Rule 4 of 13 · Chapter I — Before You Point at a Number
Check how much of the number one person or team can move unilaterally, and expect it to decay in proportion to that control.
Why this rule exists
Corruption of a measure requires both motive and leverage. A number that depends on many independent actors, external conditions, and data nobody owns is hard to bend even when people want to; a number that one team enters, defines, and reports is bendable by that team alone. Control is the practical predictor of how fast a metric will stop meaning what it meant.
In practice
For each candidate measure, trace who defines the categories, who enters or triggers the data, and who could change the figure in a week without anyone else's agreement. Prefer measures where those roles sit with different people, or where the data is produced as a by-product of a process rather than reported into it. Where high unilateral control is unavoidable, treat the metric as short-lived and schedule a review of it from the start.
When it doesn't apply
Measures used purely for a team's own diagnosis, with no external consequences attached, can sit entirely under that team's control — the risk returns the moment anyone else reads them to judge.