Rule 8 of 13 · Chapter II — Building Measures That Survive Attention
Give every metric an expiry date, and make it re-earn its place or retire.
Why this rule exists
Measures accumulate. Each one that outlives its question keeps drawing effort and reporting time, and the older it is, the more thoroughly the organisation has learned to produce it cheaply rather than honestly. An expiry date forces the review that nobody ever volunteers to run, and retires the metrics that have quietly become rituals.
In practice
Record a review date with the metric itself — six or twelve months is usually right — and at that date make someone argue for renewal: what decision did this number change, what would we have done differently without it, has the gap between the number and the thing it stands for widened? Default to retirement if no one can answer. Archive the history so you can still look back, but stop collecting.
When it doesn't apply
Metrics tied to statutory reporting or long-horizon trends need continuity more than they need freshness, and breaking a decade-long series to prove a point is a bad trade. Review those for integrity rather than for survival.