Goodhart's Law
A closely-related effect I often cite is the McNamara fallacy[0], which is essentially about the tendency to focus on aspects of a system that are easily measurable, often at the expense of aspects that are not.  I see it as one of the weaknesses of the data-driven decision-making movement, since many interpret "data" to mean "numbers".  I think this fallacy can partly explain why Goodhart's Law holds: it's the non-measurable (or difficult-to-measure) aspects that suffer most when a metric becomes a target, since measurable aspects could be (and often are) integrated into the target metric.[0]: https://en.wikipedia.org/wiki/McNamara_fallacy