Overfitting and the strong version of Goodhart’s law
This keeps getting rediscovered in new domains.<p>JIT was the savior of manufacturing, until people learned that a single traffic jam that delayed a single delivery could create costs far in excess of the inventory savings.<p>Optimizations are critical, everywhere. And measuring optimizations is important because it is is easier and cheaper and earlier than measuring end results. Measuring days of inventory, or dollars in inventory, is a pretty good proxy for supply chain efficiency, until covid hits and suddenly “efficiency” means stability rather than minimum costs.<p>Over and over. Branch prediction / Spectre. Mortgage-Backed Securities. Optimizations based on second- and third-order effects blow up in the real world where any abstraction is approximate.<p>So it’s not the efficiency that’s the problem, it’s changing the focus from maximizing the desired output to maximizing efficiency, and measuring success based on the performance of efficiency optimizations.