Five years ago, who would have predicted that the rich world would reprise the Great Depression?

And yet here we are. The surprising frequency of the "unthinkable" happening suggests we are overly confident in our ability to see the future. The "risk-parity" approach to portfolio construction is a powerful way to combat this mistake. Pioneered by Bridgewater Associates, modern risk-parity portfolios adhere to a simple principle: balance exposures across all the major economic scenarios by volatility. The hope is that such a portfolio will perform well in all economic climates--and indeed risk-parity strategies have.

The strategy is gaining influential adherents, mainly among institutions, but hasn't caught on with individuals. Will this strategy work in the future? Could an individual investor apply it? I think the answer is, tentatively, yes to both questions. To understand why risk-parity works, we have to revisit a common fundamental misconception of portfolio construction.

The typical investor thinks of assets as being like indivisible elements, with distinct characteristics. In contrast, the risk-parity approach begins with the observation that asset classes can be described in much the same way atoms can be described as combinations of electrons, protons, and neutrons. The fundamental particles in the risk-parity view of the world are inflation and economic growth. This isn't a modern insight, but one that's been around academia for decades. The risk-parity application is relatively new, however.