The reasons for the 1929 Wall Street crash and why it occurred at the particular time that it did are still debated among economic historians. We contribute to this debate by building on a new model, which provides a measure of the financial system's potential for financial crises. The evidence suggests that a tightening of margin requirements in the first nine months of 1929 combined with price declines in September and early October caused enough investors to become constrained that the market was tipped into instability, triggering the sudden crash of October and November. 

Analyzing a large sample of U.S. firms, we show that the asymmetry of stock return volatility is positively related to investor attention and differences of opinion. Using the number of analysts following a given firm to capture attention and the dispersion in analyst forecasts as a common proxy for differences of opinion, we show that the two effects are complementary. Furthermore, the effect of attention is strongest among stocks with low institutional ownership and high idiosyncratic volatility. Our results are robust to the traditional “leverage effect” explanation of volatility asymmetry. The findings relate to the previously documented relationship between attention and volatility and suggest that volatility asymmetry is driven by asymmetric attention.