“While I was at CalPERS, concerns arose in 2016 about the effectiveness of standard portfolio diversification as prescribed by Modern Portfolio Theory. We began to recognize that management of portfolio risk and equity tail risk, in particular, was the key driver of long-term compound returns. Subsequently, we began to explore alternatives to standard diversification, including tail-risk hedging. At present, the need to rethink basic portfolio construction and risk mitigation is even greater — as rising hope in Modern Monetary Theory to support financial markets is possibly misplaced……”
A good read about why bonds might no longer be used for what they were intended for historically in portfolio construction.