Comment by godelski

  > in the context of the law

That's the key part. The metric has context, right?

And that's where Goodhart's "Law" comes in. A metric has no meaning without context. This is why metrics need to be interpreted. They need to be evaluated in context. Sometimes this context is explicit but other times it is implicit. Often people will hack the metric as the implicit rule is not explicit and well that's usually a quick way to make those rules explicit.

Here's another way to think about it: no rule can be so perfectly written that it has no exceptions.