Why History Does (Not) Repeat Itself
Before we dive into individual theory families, a fundamental clarification is worthwhile: What are cycles at all — and what are they not? Three terms are regularly conflated in trading literature:
- Cycles — recurring patterns with approximate periodicity, driven by structural mechanisms (inventory, debt, demographics, generations).
- Trends — directional movements without the assumption of recurrence (secular bull markets, tech-adoption S-curves).
- Random Walks — the null hypothesis of the efficient market hypothesis: prices are unpredictable, every pattern is pareidolia.
Pattern recognition has historically been sometimes extremely useful: those who recognized parallels to earlier crashes in 1929 could anticipate the 1932 bottom — and capture the subsequent 1950s rebuilding bull market. Those who classified the 2008 subprime crisis as a classic debt deleveraging phase bought into the ensuing bull market in 2013. The COVID crash of March 2020 also ended after six weeks in a V-shape recovery that only those who understood central-bank reaction functions as a cycle component expected.
Just as often, however, pattern recognition fails spectacularly: Japan's Nikkei hit an all-time high in 1989 and took more than three decades to return — every cyclical recovery forecast of the 1990s and 2000s was wrong. The dotcom bull market of 1999 looked like a classic bull trap, but ran for another twelve months and ruined many early shorts. And the V-shape pattern of 2020 was a shock to most classical business-cycle models — they predicted an L or U shape.
The core message of this chapter: cycle theories are a useful framework for structuring market reality, but no oracle. Those who misunderstand them as prediction machines lose money. Those who use them as diversification triggers and risk-assessment aids can improve their own trading process.