Market events, and the lesson each one actually taught

Convergence trades at scale — A fund of extraordinary talent held highly leveraged convergence positions — spreads that should narrow — across many markets. When Russia defaulted, every spread widened at once, and the positions that were supposed to be diversified turned out to be the same trade in different clothing. Leverage forced selling into exactly the markets already moving against them.

Liquidity is not a constant — A large automated sell programme in index futures, sized as a share of *volume* rather than of liquidity, executed into a thinning book. Market makers withdrew, volume rose as machines traded with each other, the algorithm sped up in response, and prices in some names briefly printed at a cent. The lesson is that liquidity is an equilibrium outcome, not a property of the market you can assume.

Rules-based flow that must chase — Inverse-VIX products held short VIX futures and rebalanced daily to a constant exposure — so when volatility rose they had to *buy* VIX futures, into a market already moving against them. The flow was large relative to the contract, mechanical, and perfectly predictable to anyone who had read the prospectus. Several products lost most of their value in a single afternoon.

Physical delivery is physical — The expiring WTI contract settled at minus $\$37$. Holders who could not take delivery had to pay someone to take the contract, because storage at Cushing was full and the futures contract obliges physical delivery. Nothing was broken: the price of a barrel you must receive and cannot store is genuinely negative, and several risk systems that assumed prices were non-negative could not represent it.

Short squeezes and gamma — Heavy short interest met concentrated retail call buying. Dealers short those calls had to buy stock to stay hedged, and buying more as the price rose — a gamma feedback loop — while short sellers covering added to the same flow. Brokers then restricted buying because clearing-house margin requirements rose with volatility, which is the part most commentary got wrong.