Contrary to popular belief, earnings growth has a very low correlation with decadal stock returns. The primary driver is the change in the valuation multiple (e.g., P/E ratio expansion or contraction). The correlation between 10-year real returns and 10-year valuation changes is a staggering 0.9, while it is tiny for earnings growth.

While institutional capital market assumptions align with objective, yield-based models, their actual portfolio actions can deviate. Many institutions, despite models suggesting caution on expensive US stocks, maintained market weight, benefiting from the prolonged bull market. This highlights a critical inconsistency between their stated process and real-world behavior.

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.

Post-mortems of bad investments reveal the cause is never a calculation error but always a psychological bias or emotional trap. Sequoia catalogs ~40 of these, including failing to separate the emotional 'thrill of the chase' from the clinical, objective assessment required for sound decision-making.

The market for financial forecasts is driven by a psychological need to reduce uncertainty, not a demand for accuracy. Pundits who offer confident, black-and-white predictions thrive because they soothe this anxiety. This is why the industry persists despite a terrible track record; it's selling a feeling, not a result.

Michael Mauboussin argues the market is inherently long-term oriented. For major Dow Jones stocks, nearly 90% of their equity value is derived from expected cash flows beyond the next five years, debunking the common narrative of market short-sightedness and a focus on quarterly results.

Investors often invent compelling secular narratives—like a permanent housing shortage or "Zoomers don't drink"—to justify recent price movements. In reality, these stories are frequently post-hoc rationalizations for normal cyclical fluctuations. The narrative typically follows the price, not the other way around, leading to flawed trend extrapolation.

Moving from science to investing requires a critical mindset shift. Science seeks objective, repeatable truths, while investing involves making judgments about an unknowable future. Successful investors must use quantitative models as guides for judgment, not as sources of definitive answers.

Quoting G.K. Chesterton, Antti Ilmanen highlights that markets are "nearly reasonable, but not quite." This creates a trap for purely logical investors, as the market's perceived precision is obvious, but its underlying randomness is hidden. This underscores the need for deep humility when forecasting financial markets.