Goodhart's law

Goodhart's law is an observation about organizational control that "When a measure becomes a target, it ceases to be a good measure."

It was formulated by economist Charles Goodhart in 1975, and popularized in this phrasing by anthropologist Marilyn Strathern in 1997. The moment a metric is tied to compensation, performance evaluations, or quarterly status reports, people stop managing the business and start managing the score.

• Tell developers they are measured by lines of code, and you get bloated, unmaintainable systems.
• Measure QA by bugs closed, and trivial typos get logged while systemic architecture defects get ignored.
• Measure sales reps by calls placed, and you get hundred-call days that convert zero real customers.

Measurement was originally designed by Drucker as an instrument of self-control—a mirror to help teams evaluate their own work and adjust course. When it becomes an instrument of external surveillance, gaming the metric replaces doing actual work.