“When a measure becomes a target, it ceases to be a good measure.”
Goodheart’s Law applies to feedback system with humans in the loop. (It doesn’t apply to feed-forward systems.)
Any system including people is a kind of feedback system, because people are smart. We are agents. We observe outcomes and change behaviour in response to system pressures. evolution.
The measure will cease to be a good measure when participants become aware of it and optimise for the measure, rather than for the outcome that the measure was intended to proxy.