When a measure becomes a target, it stops measuring

In the 1970s, the economist Charles Goodhart noticed something awkward: every time the Bank of England picked an indicator to steer its policy, the indicator stopped working. The popular version of his law fits in one sentence: when a measure becomes a target, it ceases to be a good measure.

The mechanism is human, not technical. An indicator works while it is a thermometer: it reflects something that happens. The moment you turn it into a goal, people —you included— stop improving the thing and start improving the number. The school that trains for the test instead of teaching. The website that chases clicks and buries what was worth reading. Your step counter, and you circling the living room at eleven at night.

The antidote is not to stop measuring: it is to trust the scoreboard a little less. Three tricks: ask what the number was meant to capture before it became a goal; glance now and then at another measure you are not chasing; and revise the target the moment you notice you have learned to play it. The number was a map. Don't mistake it for the territory.