Investors are understandably nervous. Markets don’t like uncertainty. And what could be more bone-chilling than a seemingly out-of-control virus leaping from region to region around the globe, without a known vaccine to prevent it or slow it down, causing death and economic mayhem along the way? The coronavirus narrative has the texture and feel of “The Andromeda Strain,” the 1969 science-fiction thriller, come to life.

And so, in typical fashion, last week the equity markets reacted by plunging, in what seemed like a free-fall, before recovering somewhat today. Look past the initial shock, and one thing is clear: Investors’ legitimate concern about the spread of the coronavirus is the best thing to happen to the U.S. stock markets since Donald Trump became president.

Last week’s mantra was, “Take your profits immediately; ask questions later.” That meant there were many more sellers in the equity markets than buyers. The Dow Jones industrial average dropped a debilitating 12 percent in five trading days. Other equity markets followed suit.

And then there was another equally predictable reaction: the flight to safety. Investors poured into Treasury securities, driving their yields down to the lowest levels on record. Since mid-February, the yield on the 10-year Treasury bond has dropped to around 1.08 percent, from 1.6 percent, a big move in a short time. Then investors, as well as the president of the United States, called for more painkillers, demanding that the Federal Reserve lower short-term interest rates beyond their already low levels.