Goodhart’s Law
What it is
Goodhart’s Law is commonly summarized as:
When a measure becomes a target, it ceases to be a good measure.
The idea is usually attributed to British economist Charles Goodhart, who expressed the core insight in the context of monetary policy: once pressure is placed on a statistical regularity for control purposes, the regularity tends to break down. Later writers generalized the idea into the better-known wording about measures becoming targets.
In plain language: when people know a number matters, they begin responding to the number.
And once people begin responding to the number, the number may stop representing the thing it was originally meant to measure.
Why it matters to MNKY Math
Goodhart’s Law lives very close to the center of MNKY Math.
MNKY Math is interested in what happens after a metric enters a system and people, incentives, tools, and processes begin adapting around it.
- A metric can begin as a signal.
- Then it becomes a target.
- Then it becomes a pressure.
- Then behavior starts changing around the pressure.
At that point, the metric is no longer only measuring the system. The metric is now participating in the system.
Where we overlap
Goodhart’s Law and MNKY Math both care about the gap between measurement and meaning.
They overlap around questions like:
- What changes when a measure becomes a target?
- How do incentives reshape behavior?
- When does a metric stop representing the outcome it was meant to protect?
- How can a number improve while the system gets worse?
- What behavior is the system learning to produce?
Goodhart’s Law is especially useful when examining metric distortion, gaming, performative compliance, target-chasing, and measurement systems that begin replacing the outcomes they were supposed to represent.
Where MNKY Math differs
Goodhart’s Law is often used as a warning about metrics.
MNKY Math treats that warning as one part of a larger system.
The question is not only: Did the measure become a bad measure?
MNKY Math also asks:
What did the system begin teaching once the measure became important?
That means MNKY Math looks beyond the metric itself and examines the wider loop: the system, the signal, the incentive, the participant, the behavior, the hidden tradeoff, and the outcome that emerges over time.
Goodhart’s Law helps explain why the number may stop being trustworthy.
MNKY Math asks what the system becomes while trying to make the number look right.
How it shows up
Goodhart’s Law can appear almost anywhere measurement becomes pressure.
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A customer-service team may optimize call time while weakening customer experience.
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A company may chase engagement scores while employees learn to perform engagement.
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A school may improve test scores while narrowing learning.
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A sales team may hit activity targets while reducing the quality of customer conversations.
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A workplace may reach survey participation goals while missing what the participation push already revealed about trust.
In each case, the metric may move.
But the movement does not automatically mean the system improved.
MNKY Math lens
Goodhart’s Law helps name the moment when measurement starts changing the thing being measured.
MNKY Math extends the lens by asking:
- What behavior did the measurement teach?
- What outcome did the system actually produce?
- What tradeoff moved somewhere else?
- What became easier to defend because the number looked right?
Relationship map
Closest twin: Campbell’s law Both examine what happens when measurement becomes pressure, but Goodhart’s Law focuses more on the measure losing usefulness.
Clarifying contrast: Cobra Effect Cobra Effect focuses on incentives that worsen the problem; Goodhart focuses on metrics that stop representing what they were meant to measure.
Mostly shaped by: Measurement Goodhart’s Law begins when a measure is used as a target or control mechanism.
Helps explain: Metric-Outcome Gap It helps explain why hitting the number may no longer mean achieving the intended outcome.