After a decade of negative real returns, bonds are now attractive on a pure valuation basis relative to equities. PIMCO's CIO suggests bonds may outperform stocks over the next 5-10 years, making a compelling case for allocation regardless of their traditional role as a correlation hedge.

Investors' equity allocations are high, not necessarily from new purchases, but from strong market performance. This passive 'drift' creates a significant, often overlooked, concentration risk. This means many portfolios are more exposed to an equity drawdown than their owners may realize, necessitating a review of diversification strategies.

A fundamental reason for differing investor behavior is the unit of discussion. Bond investors focus on forward-looking yields, which naturally fosters a contrarian, mean-reverting mindset. Equity investors focus on backward-looking prices and returns, leading them to extrapolate recent trends and chase momentum.

Unlike institutions that focus on spreads, a large and growing segment of retail investors cares only about absolute yield. This creates a durable source of demand, as these investors tend to buy into weakness when yields rise, preventing the sustained outflows and sharp sell-offs seen in past cycles.

The primary role of a small fixed-income allocation (e.g., 10%) isn't to generate returns but to act as a behavioral stabilizer. It provides a simple, mechanical rebalancing rule: trim equities if bonds fall to 5%, buy more if they rise to 15%. This forces disciplined "buy low, sell high" behavior.

The entire modern financial system was built on the historically anomalous assumption of a negative correlation between stocks and bonds. The market is now reverting to its historical norm of positive correlation, invalidating traditional portfolio construction like 60/40.

While lauded for its simplicity, the three-fund Boglehead portfolio reveals a key weakness in environments like 2022. Its lack of exposure to truly uncorrelated assets like cash means investors suffer when its core components fall in unison. A portfolio can be "too simple."

The historical negative correlation between stocks and bonds, which underpins the 60/40 portfolio, breaks down when inflation rises above 2%. In this environment, they tend to move together, making bonds an ineffective diversifier and forcing investors to seek new solutions for equity risk.

For 40 years, falling rates pushed 'safe' bond funds into increasingly risky assets to chase yield. With rates now rising, these mis-categorized portfolios are the most vulnerable part of the financial system. A crisis in credit or sovereign debt is more probable than a stock-market-led crash.