Investors extrapolating future returns from recent performance is a more damaging force in markets than underestimating fat tails or the rise of passive indexing. This behavior of 'return chasing' hurts individual investors the most and leads to poor resource allocation.

Mathematical models like the Kelly Criterion are only as good as their inputs. Historical data, such as a stock market's return, isn't a fixed 'true' value but rather one random outcome from a distribution of possibilities. Using this single data point as a precise input leads to overconfidence and overallocation of capital.

The 60/40 portfolio is obsolete because bonds, laden with credit risk, no longer offer safety. A resilient modern portfolio requires a broader mix of uncorrelated assets: cash, gold, currencies, commodities like oil and food, and short-term government debt, while actively avoiding corporate credit.

While long-term focus is a virtue, investment managers at WCM warn it can become an excuse for inaction. During periods of significant market change, blindly "sticking to your knitting" is a liability. Recognizing when to sensibly adapt versus when to stay the course is a critical and nuanced skill.

Conventional definitions of risk, like volatility, are flawed. True risk is an event you did not anticipate that forces you to abandon your strategy at a bad time. Foreseeable events, like a 50% market crash, are not risks but rather expected parts of the market cycle that a robust strategy should be built to withstand.

Judging investment skill requires observing performance through both bull and bear markets. A fixed period, like 5 or 10 years, can be misleading if it only captures one type of environment, often rewarding mere risk tolerance rather than genuine ability.

Howard Marks argues that you cannot maintain a risk-on posture and then opportunistically switch to a defensive one just before a downturn. Effective risk management requires that defense be an integral, permanent component of every investment decision, ensuring resilience during bad times.

Long-term economic predictions are largely useless for trading because market dynamics are short-term. The real value lies in daily or weekly portfolio adjustments and risk management, which are uncorrelated with year-long forecasts.

Howard Marks offers a crucial corollary to Einstein's famous quote. For investors, the real insanity is failing to recognize a paradigm shift. Applying strategies that worked during 40 years of falling interest rates to the current, different environment is a recipe for failure. The context determines the outcome.