Guard against gaming the number

Any lone target invites Goodhart's Law

The moment you elevate a single number to the thing the organisation steers by, you create an incentive to make that number go up by whatever route is easiest, including routes that destroy value. This is Goodhart's Law, the well-worn observation that a measure which becomes a target stops being a good measure, and it is the most serious risk in the whole exercise.

The failure is concrete and quiet. You pick signups as your star, the team optimises signups, signups climb, and underneath the rising line churn worsens, real usage thins out, and quality rots, because nobody was watching those things and the star did not require them to. The number genuinely went up. The business genuinely got weaker. Tunnel vision around a single target is how an organisation optimises itself into trouble while every report looks green.

Choosing one number is a real risk, taken on purpose

It is worth being honest that committing to a single company-wide metric is inherently risky if you pick the wrong one. That is not an argument against having a north star, it is an argument for choosing it with the care this playbook describes, naming your game and motion and stage rather than borrowing, and then watching it for the gaming behaviour Goodhart's Law guarantees will appear.

Watch the number that would betray the gaming

The practical defence is to never let the star travel completely alone. Pair it with a small number of counter-metrics, the figures that would move in the wrong direction if someone were juicing the star at the expense of real value. If your star is an activation or usage measure, watch churn and support load beside it. If your star is a delivered-outcome measure, watch the cost of delivering it. A star that climbs while its counter-metric quietly worsens is not a win, it is the gaming the law warned you about, caught early.

The input tree from the previous chapter and these counter-metrics together turn a single exposed number into something an organisation can actually be trusted to chase. The star sets the direction. The inputs give everyone a job. The counter-metrics keep the whole thing honest. Without that structure a north star is a Goodhart trap waiting to spring; with it, it is the clearest steering instrument a lean company can have.