Disclosure: this post was written with the assistance of an AI system (Claude), which wrote the analysis code, ran the experiments and drafted the text. The topic, the constraints, the data choices and the final review are the author’s. The ten largest S&P 500 companies are around 41% of the index against roughly 19% in 1990, and the usual conclusion is that index investors are no longer diversified. There is a formula for that....
Disclosure: this post was written with the assistance of an AI system (Claude), which wrote the analysis code, ran the experiments and drafted the text. The topic, the constraints, the data choices and the final review are the author’s. On 31 July 2026 the KOSPI rose 17.91%, the largest one-day gain in its history, and Korean individuals net sold a record 8.2543 trillion won into it. So I priced the rule: selling every 15% drawdown cost 2....
Disclosure: this post was written with the assistance of an AI system (Claude), which wrote the analysis code, ran the experiments and drafted the text. The topic, the constraints, the data choices and the final review are the author’s. On 31 July 2026 the KOSPI rose 17.91% in a single session, the largest one-day gain in its history, days after a circuit breaker halted trading and inside the second-worst month the index has ever had....