This isn’t intended as a rant against the practice of diversification – nothing could be further from the truth. But, like all popular investment tools, there’s a mythology that’s been created around modern portfolio theory to suggest a panacea to cure all ills. It’s peddled as a fairy tale that ends with investor & portfolio happily ever after – together on a horse, riding off into the sunset. My argument is that the benefits of diversification depend on having appropriately calibrated priors. And when those priors are dramatically altered, it’s time to reassess – not double-down.