Goodhart's law is often confused with Campbell's law.
The two are indeed very similar, and often used interchangeably, but there's an important difference in their phrasing.
Goodhart's law states that: "When a measure becomes a target, it ceases to be a good measure."
Campbell's law states that: "The more any quantitative social indicator is used for social decision-making, the more subject it will be to corruption pressures and the more apt it will be to distort and corrupt the social processes it is intended to monitor."
In other words, the former focuses on the fact that, while metrics sound good in theory, in practice they cannot be relied on; whereas the latter focuses on the fact that enforcing metrics in an attempt to control a social process tends to backfire.
The two are indeed very similar, and often used interchangeably, but there's an important difference in their phrasing.
Goodhart's law states that: "When a measure becomes a target, it ceases to be a good measure."
Campbell's law states that: "The more any quantitative social indicator is used for social decision-making, the more subject it will be to corruption pressures and the more apt it will be to distort and corrupt the social processes it is intended to monitor."
In other words, the former focuses on the fact that, while metrics sound good in theory, in practice they cannot be relied on; whereas the latter focuses on the fact that enforcing metrics in an attempt to control a social process tends to backfire.
Or, in Trump language:
Goodhart = "Sounds good, doesn't work"
Campbell = "Worst trade deal ever"