Far from universally true. IQ tests like the SAT, GRE, GMAT etc. are all designed to be as close to ungameable as possible. There’s a limited amount they can do but the limit is very high indeed. The major, and unavoidable defect is the practice effect. The more you do something the better you get at it. But IQ tests are like running or weightlifting, there are beginner gains, there are tough gains that are ground out with a great deal of effort and there’s a limit you’re not going to surpass no matter how hard you try. O matter how many steroids I take or how hard I train I’m not going to beat Usain Bolt in the 100m. I’m probably not going to beat the average NHL player.

Goodhart’s Law is the opposite of true in quality control. What gets measured gets managed. Manufacturing defects in semiconductors, automobiles and I presume, most everything else have been trending down for decades. Businesses have KPIs for employees for a reason. Monomaniacal focus over a long period on one measure may not be the best idea, but it’s a great tool to have.

This is a great example of Goodhart's Law, though. If nobody studied for the SAT, it might (arguably) work fine as a measurement of collegiate potential. But because it became the metric for collegiate success, and because the "practice effect" means that practicing makes you do better on the test, many people study hard for it and greatly increase their likely score. The folks who don't study as much or as effectively for it for whatever reason will not do as well, as so you're left with a measurement of whether people studied for the SAT and not whether the test taker would be likely to succeed at college. So a good metric becomes a bad metric because it's chosen as the metric.