Investing First Principles

Defend the indexing-dominates argument with three independent lines of evidence (Sharpe's arithmetic, SPIVA's empirical record, the behavioral data). Understand the limits of the efficient-market hypothesis without abandoning the conclusion. Name the decision biases that destroy retail returns and the specific guardrails you're committing to. Distinguish risk from volatility. Produce a dated, one-page Investing Posture document for the next decade. Active-vs-passive is build-vs-buy. In software you ask: am I solving a problem so specific that off-the-shelf doesn't fit, or am I about to spend six months reinventing a wheel because I believe I'm above-average? Most engineers, asked with founder discipline, default to buy. The same engineers, undisciplined, default to build. Module 2 makes the question explicit and lets your existing build-vs-buy instincts answer it. Marks's risk-vs-volatility distinction is production-incident-vs-noise. Volatility is page-load latency variance — annoying, normal, reverts. Risk is the data-corruption event that permanently costs you customers. Most retail investors page themselves on latency variance and sleep through the corruption. React to risk; ignore volatility. You already run this discipline in production. Apply it to the portfolio.