According to @CNBC, former Treasury Secretary and ex-Goldman Sachs chair Robert Rubin urged investors to keep the October 1987 Black Monday crash in mind as a present risk cue for markets, highlighting downside scenarios worth considering for positioning. Source: CNBC. The 1987 crash saw the Dow Jones Industrial Average plunge 22.6 percent in a single day and led to the adoption of market-wide circuit breakers that continue to govern equity selloffs. Sources: Federal Reserve History and U.S. Securities and Exchange Commission. For crypto traders, equity stress has historically transmitted to digital assets as correlations with U.S. stocks rose markedly after 2020, increasing downside risk to BTC and ETH during risk-off shocks. Source: International Monetary Fund.

According to @StockMKTNewz, the top single-day S&P 500 losses span from -20.5% on Oct 19, 1987 to -8.9% on Dec 1, 2008 and Jul 20, 1933, based on a list of the 10 worst sessions by percentage drop; source: @StockMKTNewz on X — x.com/StockMKTNewz/status/1979927056944128509. According to @StockMKTNewz, these extremes cluster around 1929–1937, 2008, and March 2020, indicating historically concentrated shock regimes that traders can reference when calibrating downside scenarios; source: @StockMKTNewz on X — x.com/StockMKTNewz/status/1979927056944128509. According to @StockMKTNewz, a practical takeaway for equities, cross-asset, and crypto risk monitoring is to stress-test single-day equity shocks in the roughly -10% to -20% range derived from the listed events; source: @StockMKTNewz on X — x.com/StockMKTNewz/status/1979927056944128509.

According to @StockMKTNewz, on October 19, 1987, the S&P 500 fell 20.5% and the Dow Jones dropped 22.6% in a single session, marking the worst day in U.S. stock market history known as Black Monday (source: @StockMKTNewz). In response, U.S. regulators implemented market-wide circuit breakers that now pause trading at S&P 500 declines of 7%, 13%, and 20% to curb disorderly moves (source: NYSE; SEC). For crypto traders, major equity selloffs have been associated with higher BTC–equity correlations, making these trigger levels useful risk markers, while CME Bitcoin futures also employ price limits and velocity logic that can pause trading during extreme moves (source: IMF; CME Group).