Investors try to apply lessons from past market cycles, but this collective awareness changes their behavior. This creates a self-reinforcing loop that alters timelines and dynamics, ensuring history only rhymes, not repeats.

An investor's lived experience can be a poor guide to long-term market realities. For example, someone who started their career after 2009 has only known a US stock market that consistently rewards dip-buying, a pattern not representative of broader history.

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.

The historical outperformance of stocks has a standard error so large (2.1% on a 5.4% premium) that the true premium could be anywhere from 1% to 9%. This statistical uncertainty makes history an unreliable guide for future returns.

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.

Absolute truths are rare in complex systems like markets. A more pragmatic approach is to find guiding principles—like "buy assets for less than they're worth"—that are generally effective over the long term, even if they underperform in specific periods. This framework balances conviction with flexibility.

Timing is more critical than talent. An investor who beat the market by 5% annually from 1960-1980 made less than an investor who underperformed by 5% from 1980-2000. This illustrates how the macro environment and the starting point of an investment journey can have a far greater impact on absolute returns than individual stock-picking skill.

Most investors evaluate performance over a few years, but financial economist Ken French states it's 'crazy' to draw inferences from three, five, or even ten-year periods for an active fund. Shorter timeframes are heavily influenced by randomness and luck, leading to flawed investment decisions.

Across 200 years and 56 countries, the single most important factor for long-term investing success is the starting valuation. Buying portfolios with low P/E ratios or high dividend yields consistently outperforms buying expensive assets by 3-4% annually over the long run.