What is an example of Goodhart's law?

Paying programmers per line of code produces bloated, padded code. The metric (lines) is hit while the goal (good software) suffers, because the reward is attached to the measure, not the outcome.

How do you avoid Goodhart's law?

Use multiple metrics that are hard to game together, pair targets with counter-metrics, and keep checking whether the number still reflects the underlying goal. Treat any single optimised metric with suspicion.

Goodhart's law

Economics & measurement

Goodhart's law states that when a measure becomes a target, it ceases to be a good measure. Once people are rewarded for a metric, they optimise the metric itself — often at the expense of the real goal it was meant to track.

How it works

Whenever you set a target or KPI, distinguish the metric from the underlying goal it stands for. Then ask how people could hit the number without achieving the goal — and assume they eventually will, because incentives reward the measure, not the intention.

How to use it

Designing metrics and targets that are hard to game, or pairing them with counter-metrics.
Diagnosing why a once-useful KPI has stopped reflecting reality.
Staying sceptical of any system optimised toward a single number.

Worked example

A hospital judged on ER wait times starts logging patients as "seen" the moment a nurse greets them, or keeps ambulances queued outside. The wait-time metric improves while actual care doesn’t — the target corrupted the measure.

Where it fails

The lesson isn’t "never measure" — you need metrics to manage. The error is trusting any single metric too much. Over-correcting into metric-phobia leaves you flying blind; the fix is better, harder-to-game measures, not none.

The deeper point

It is the reason almost every dashboard eventually lies. The moment a number controls rewards, it starts measuring people’s ingenuity at hitting numbers — which is why the most-optimised metric in any organisation is usually the least trustworthy.

Frequently asked

What is Goodhart's law?: It states that when a measure becomes a target, it stops being a good measure. Once people are rewarded for a metric, they optimise the metric itself — often undermining the real goal it was meant to capture.
What is an example of Goodhart's law?: Paying programmers per line of code produces bloated, padded code. The metric (lines) is hit while the goal (good software) suffers, because the reward is attached to the measure, not the outcome.
How do you avoid Goodhart's law?: Use multiple metrics that are hard to game together, pair targets with counter-metrics, and keep checking whether the number still reflects the underlying goal. Treat any single optimised metric with suspicion.

Incentives Second-order thinking Systems thinking

Editorial synthesis © ReadGlobe 2026, drawing on the mental-models tradition (Charlie Munger, Farnam Street) and the primary sources for each model. · Last reviewed 2026-05-29.