Goodhart's Law

How it works

When a measure becomes a target, it ceases to be a good measure.

This model helps you recognise situations where this pattern is at play and adjust your thinking accordingly. Understanding it does not make you immune, but it gives you a framework for catching it in action and making better decisions as a result.

Case study: How Soviet nail factories optimised for the wrong metric

A famous (possibly apocryphal but illustrative) story from Soviet central planning: when Moscow set production targets for nail factories by weight, the factories produced enormous, unusable nails. When the target was changed to quantity, they produced millions of tiny, useless tacks.

The factories weren’t failing. They were succeeding — at the metric, not the mission. The goal was useful nails. The measure was tonnage (or count). The moment the measure became the target, it ceased to measure what mattered.

Every modern organisation faces the same dynamic. Schools measured by test scores teach to the test. Hospitals measured by readmission rates avoid admitting risky patients. Software teams measured by lines of code write verbose code. The metric optimises itself at the expense of the actual goal.

When to use it

Apply this model whenever you notice its pattern appearing in your decision-making, your team’s behaviour, or the systems around you. It is especially valuable in high-stakes situations where the cost of this error is significant.

Try it now

Think of a recent decision or situation where this model might have been relevant. How would your approach have changed if you had explicitly considered it?