Henry Neville of Man Group asks a question that every serious investor should sit with: what happens when the rules you have trusted for decades quietly stop working? In a recent essay published October 8, 2026, Neville revisits three of the most durable heuristics in investment practice and subjects them to an honest reckoning. The title, drawn from the Book of Daniel, sets the tone. The Law of the Medes and Persians could not be revoked, even by the king who wrote it. Neville's argument is that some investment rules may be approaching that kind of rigidity, and rigidity, in markets, can be its own form of risk.
The Yield Curve Signal Is Fading
The inversion of the 10-year/2-year US Treasury spread has long been treated as a reliable recession harbinger. The logic is clean: banks borrow short and lend long, so an inverted curve is a disincentive to lending, a tightening of credit, a headwind to growth. Neville acknowledges the intuitive force of this, noting that "10 out of 10 historic recessions experienced an inversion in the 24 months prior." But the most recent inversion began in July 2022, dove to depths not seen since the early 1980s, and, more than four years later, no recession has arrived.
Neville points to structural forces that may be distorting the signal: the weaponisation of the dollar, fiscal dominance, the merging of monetary and fiscal authorities, geopolitical pressure on the Treasury market. Whether these represent "real forces, or just column inches and chin scratching," he writes, it is "feasible" that the US yield curve is no longer a clean proxy for the capital cost and growth interaction it once measured. His verdict is measured but definitive: "It's gone from being a biomarker of terror, to a bit more than a raised eyebrow."
For advisors, this matters. The inversion-to-recession framework has shaped defensive positioning and client conversations for years. A signal that has weakened demands corresponding adjustment in how much weight it receives.
Valuation: The Tool May Have Outlived Its Calibration
Neville is careful here. He is not arguing that intrinsic value does not exist. He is arguing that the instruments used to measure it may be badly dated. The Fama-French HML factor, which captures the excess return of high-book-value stocks over low-book-value stocks, compounded at 5% annually from 1926 to 2006. Since then, the equivalent figure is negative 2%. "All alpha tends to codify eventually, and then it's just beta," Neville observes. "Perhaps this dog has had its day."
The deeper question is definitional. Neville poses it sharply: "What do we even mean by valuation?" If the answer is some objective measure of true worth that markets will eventually recognise, the concept survives. If the answer is a specific ratio that Graham and Dodd considered meaningful eighty years ago, before spreadsheets existed, before platform-era companies rewrote what an economic moat looks like, the case becomes shakier. SpaceX, trading at 110x forward earnings today but 15x 2030 consensus, is his bellwether. A small probability of a very large payoff, in an industry with essentially a single public-market proxy, strains classic multiples. "As things get massive," he asks, "are classic valuation multiples still adequate descriptors?" The honest answer is: probably not always.
Neville is not throwing valuation discipline overboard. He remains nervous about stretching multiples, mindful of the Dot-Com lesson. But he is "open to making a little more room in the portfolio, at least than I would previously, for these kind of euphoria-multiples."
Stock-Bond Correlation: Carry Changes the Math
The third rule under examination is the idea that positive stock-bond correlation makes fixed income useless as equity insurance. Neville agrees the positive correlation regime is real and will persist. But he resists the conclusion that bonds are therefore dead in a portfolio context. The correlation coefficient, he notes, "can cover a multitude of sins." One such sin: assets can be positively correlated over long periods yet negatively correlated during the short, acute windows that actually test a portfolio.
More importantly, carry has re-entered the equation. Across 15 US equity drawdowns exceeding 25% over the past century, bonds produced positive returns in eight of the 11 that occurred against a positive correlation backdrop. The 1980-82 episode is illustrative: even through one of the most aggressive tightening cycles in history, the 10-year Treasury delivered an 18% total return while equities fell 27%. With yields now at levels not seen in a generation, Neville invokes the movie villain Hans Gruber's dream of "sitting on a beach, earning twenty percent" to make his point: carry is back, and "chunky yields are now a part of the portfolio construction playbook."
Five Key Takeaways for Advisors and Investors
- The yield curve inversion is no longer a reliable recession timer. Structural distortions in the Treasury market may have permanently diluted the signal. Weight it accordingly, not as a primary trigger.
- Valuation tools built for a pre-digital, pre-platform economy need recalibration. The failure of classic value factors since 2006 is not noise; it warrants intellectual openness to different measurement frameworks.
- Positive stock-bond correlation does not eliminate fixed income's defensive role. In acute drawdowns, the combination of duration and carry has historically delivered. The picture is messier, but not broken.
- Carry is a portfolio variable again. At current yield levels, fixed income contributes real income buffer against equity volatility, a dynamic that was effectively absent for most of the 2010s.
- The discipline of reviewing base truths is not tinkering; it is risk management. Rules held too long past their usefulness become their own source of exposure. The exercise Neville performs is one advisors and investors should replicate on a regular basis.
Footnote:
1 Neville, Henry. "The Law of the Medes and Persians." Man Group Insights, 8 Oct. 2026, www.man.com/insights/road-ahead-law-medes-persians.
