Goodhart's Law — When Logic Wears a Disguise

Goodhart's Law states that when a measure becomes a target, it ceases to be a good measure. Once people know they are being evaluated by a specific metric, they optimize for that metric rather than the underlying goal it was intended to represent. This creates perverse incentives where the metric improves while the actual desired outcome deteriorates or remains unchanged.

Also known as: Campbell's Law, metric gaming, teaching to the test, cobra effect

How It Works

Metrics are simplifications of complex realities. Optimizing for the simplified proxy is almost always easier than optimizing for the underlying complex goal, so rational actors will game the metric.

A Classic Example

A call center sets 'average call duration' as a key performance indicator, targeting shorter calls. Agents begin rushing customers, transferring difficult calls, or hanging up before resolution. Average call time drops, but customer satisfaction plummets and repeat calls increase.

More Examples

A school district ties teacher evaluations to student scores on standardized reading tests. Teachers begin dedicating nearly all class time to test-format drills, cutting out creative writing and critical discussion. Test scores rise, but broader literacy and love of reading decline.

A software company measures developer productivity by number of commits per week. Developers respond by breaking single logical changes into dozens of tiny, trivial commits. Commit counts soar while actual feature delivery slows down.

Where You See This in the Wild

Goodhart's Law manifests in standardized testing (teaching to the test), policing (crime statistic manipulation), scientific publishing (citation gaming), and social media (engagement metric optimization).

How to Spot and Counter It

Use multiple complementary metrics that are harder to game simultaneously. Regularly rotate or update metrics, and include qualitative assessments alongside quantitative ones.

The Takeaway

The Goodhart's Law is one of those reasoning errors that sounds perfectly logical at first glance. That's what makes it dangerous — it wears the costume of valid reasoning while smuggling in a broken conclusion. The best defense? Slow down and ask: does this conclusion actually follow from these premises, or am I just connecting dots that happen to be near each other?

Next time someone presents you with an argument that "just makes sense," check the structure. The feeling of logic is not the same as logic itself.