Black Monday: Huge Losses a Reminder of Risk

30 years ago today, global stock markets collapsed. The U.S. stock market represented by the S&P 500 had gained over 35% year-to-date. Investors were likely optimistic. It only took a single day to erase the gain.

The loss on Black Monday was -31.5%. Notice that a -31.5% decline more than erased a 35%+ gain. In fact, after the index had gained over 35% for the year, it was down nearly -9% after a -31% decline.


As I explain in Asymmetric Nature of Losses and Loss Aversion, losses are asymmetric. Losses compound exponentially, which is what makes risk management and the pursue of drawdown control worthwhile.

Below we see it in action. It only took a decline of -31% to erase over 60% of a 100% gain since 1984. The S&P 500 stock index had gained over 100% since 1984. The -31% decline brought the gain all the way down to 37%. Losses are very asymmetric.

Black Monday is talked about as a single one-day event, but really it wasn’t. Several weeks of weakness led up to a big down day. But, it would have taken a rather tight risk management system to have exited.

Looking even closer, the % off high chart shows the stock index was about -7% off its price high for several weeks before the crash. So, a drawdown control and risk management system trading this index would have had to exit because of this trend.

It doesn’t have to happen in a single day to erase a lot of gains.

Let’s remember this one.

And more recently, this one.

Today is a reminder that markets are risky and they necessarily require risk management.



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