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.

Owning multiple stocks or ETFs does not create a genuinely diversified portfolio. True diversification involves owning assets that react differently to various economic conditions like inflation, recession, and liquidity shifts. This means spreading capital across productive equities, real assets, commodities, hard money like gold, and one's own earning power.

Market-cap-weighted indexes create a perverse momentum loop. As a stock's price rises, its weight in the index increases, forcing new passive capital to buy more of it at inflated prices. This mechanism is the structural opposite of a value-oriented 'buy low, sell high' discipline.

Contrary to typical risk-off strategies, ARK Invest manages risk by concentrating its portfolio into its highest-conviction names during market downturns. Conversely, during bull markets, as opportunities like IPOs increase, the firm diversifies its holdings to capture broader upside.

A more robust diversification strategy involves spreading exposure across assets that behave differently under various macroeconomic environments like inflation, deflation, growth, and contraction. This provides better protection against uncertainty than simply mixing asset classes.

When a small, speculative investment like crypto appreciates massively, it can unbalance an entire portfolio by becoming an oversized allocation. This 'good problem' forces investors to systematically sell the high-performing asset to manage risk, even as it continues to grow.

Bridgewater's Co-CIO argues the winning formula of the last 15 years—concentrating capital in US equities and illiquid assets—is now a dangerous trap. He believes most investors have abandoned diversification because it hasn't worked recently, creating a risky setup that calls for a globally diversified portfolio.

The emotional drivers of FOMO (buying high) and panic (selling low) make the simplest investment advice nearly impossible to follow. A diversified, 'all-weather' portfolio protects against these predictable human errors better than high-risk concentrated bets.

The sign of a working diversification strategy is having something in your portfolio that you're unhappy with. Chasing winners by selling the laggard is a common mistake that leads to buying high and selling low. The discomfort of holding an underperformer is proof the strategy is functioning as intended, not that it's failing.