The stock market dropped by half in 1973-74 even while S&P 500 earnings grew by over 50%. The 1987 crash was associated with no loss in earnings. Fundamentals don't have to change overnight. There is in fact zero correlation between year-over-year changes in earnings and year-over-year changes in the S&P 500. Rather, low and expanding risk premiums are at the root of nearly every abrupt market loss.

I've noted over the years that substantial market declines are often preceded by a combination of internal dispersion, where the market simultaneously registers a relatively large number of new highs and new lows among individual stocks, and a leadership reversal, where the statistics shift from a majority of new highs to a majority of new lows within a small number of trading sessions.

This is much like what happens when a substance goes through a "phase transition," for example, from a gas to a liquid or vice versa. Portions of the material begin to act distinctly, as if the particles are choosing between the two phases, and as the transition approaches its "critical point," you start to observe larger clusters as one phase takes precedence and the particles that have "made a choice" affect their neighbors. You also observe fast oscillations between order and disorder in the remaining particles. So a phase transition features internal dispersion followed by leadership reversal. My impression is that this analogy also extends to the market's tendency to experience increasing volatility at 5-10 minute intervals prior to major declines.

Link to Hussmann Funds' website