SI402: Why Markets Can’t Stop Trending ft. Richard Brennan

— Complex adaptive systems framework — Markets operate as flocks (murmuration of starlings), not clocks. Participants follow local rules with partial information; emergent behavior (trends, cascades) arises from interactions, not central direction or external news alone.

— The endogenous engine and reflexivity — Most price movement is driven by the system processing itself, not external information. Price-sensitive participants respond to price, altering conditions for the next participant; the recursive loop sustains trends far beyond initial catalysts.

— Passive investing's structural impact — As passive capital grows (now ~60% of US equity fund assets), it reduces the population of price-sensitive, value-based agents who provide balancing feedback. Passive amplifies the reinforcing side (momentum, forced flows) while thinning resistance.

— Feedback architecture and inelasticity — Markets contain reinforcing feedback (momentum, volatility targeting, index inclusion) and balancing feedback (value investors, market makers, counter-trend traders). Passive dilutes balancing agents, making markets structurally inelastic: roughly $1 of net flow moves prices by a multiplier of 3–7×, creating larger moves per unit of capital.

— Phase transition at 25% threshold — Agent-based modeling shows markets shift from equilibrium-like behavior (Gaussian, no memory) to real-market behavior (fat tails, memory, clustering) when price-sensitive reinforcing agents reach just 20–25% of the population. This fingerprint persists across 68 futures markets, eight asset classes, 40+ years.

— Global coupling of markets — The world's futures markets are not independent; they share a persistent feedback signature because systematic investors deploy correlated models across asset classes. Cross-market coupling has averaged 0.6 (vs. 0.55 for independence) across 40 years, with no year falling to the independence baseline.

— Trend following is structural, not temporary. The 40-year empirical fingerprint of feedback-driven market behavior shows no weakening and appears identical across all asset classes and continents. Trends are not anomalies to be exploited before they close; they are a natural output of how markets actually work. Practitioners should align with, not predict, this architecture.

— Passive growth increases volatility per dollar of flow. As passive ownership rises and price-sensitive balancing agents shrink as a share of the float, the same amount of active capital produces larger price moves. The market is becoming structurally inelastic. Position sizing and risk management must account for this multiplier effect (estimated 3–7×) rather than assume historical elasticity.

— Watch the balance between reinforcing and balancing agents. Markets trend when reinforcing feedback dominates balancing feedback. As passive replaces price-sensitive discretionary capital, reinforcing forces have fewer counterweights. Monitor shifts in agent composition (e.g., passive vs. active participation rates) as leading indicators of volatility regime changes and trend persistence.