Tillinghast's investment philosophy is organized around a concept borrowed and extended from Charlie Munger: the "too hard" pile. Most opportunities in the stock market require predicting something genuinely difficult — commodity prices, regulatory outcomes, technology races, consumer taste shifts. Tillinghast argues that rational investors should consciously put these opportunities in a too-hard pile and focus on the smaller set of situations where the outcome is more analyzable.

The distinction between unpredictable and difficult is important here. Tillinghast is not saying investors should only own boring, stable businesses. He is saying they should be honest about the nature of the uncertainty they are underwriting. A company whose earnings depend on the price of oil is not simply a business bet — it is also a commodity bet. An investor who buys it without a view on oil prices has unknowingly taken a position they haven't analyzed.

"A business you actually understand" has a specific meaning in Tillinghast's framework. It means understanding the competitive dynamics, the customer economics, the cost structure, and the management incentives well enough to form an independent view on intrinsic value that differs usefully from the market consensus. Without that understanding, buying a stock is closer to speculation than investment.

This philosophy has significant practical implications for sector concentration. Investors who genuinely understand retail consumer behavior, healthcare delivery economics, or software subscription unit economics should stay in those lanes. Chasing unfamiliar sectors because they have recently performed well is a reliable path to buying high on the basis of someone else's analysis.

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