The current economic expansion is about six months from being the longest on record, he said. "They say that expansions don't die of old age, but they can die of mistakes, like a trade war or the Fed raising interest rates too high."
The market started winter the same way it roiled through the fall: Since September, the Dow has fallen nearly 4,300 points — giving up 16 percent of its value. This week accounted for more than 1,500 points of that retreat.
The Dow and the S&P 500 are both on track for their worst December performances since the Great Depression in 1931.
The sharp decline comes with the economy growing and producing jobs. And while there are threats, none seems fatal — at least not right away. But many modest dangers are starting to add up, some economists say.
There has been a slowly building trade battle with China, the issuing of modest tariffs and the talk of raising them much higher. There has been the Federal Reserve's slow, but steady campaign of rate hikes, which makes borrowing more expensive.
‘We hate the unknown’
Many corporate leaders, especially the chief financial officers who track the numbers, are worried, Cronje said. "Uncertainty is giving CFO's pause. The CFO's have really been rattled by this talk about a trade war."
All these headwinds could abate and leave growth hardly changed, but they could also grow stronger and more dangerous — and it's very hard to predict, said economist Tom Smith of Emory University's Goizueta School of Business.
The market reacts badly to these kinds of questions, he said. “It’s nervousness. People can’t take the unknown. We hate the unknown.”
Adding to the mix was this week’s federal flip-flop back and forth between a shutdown and a compromise that would keep government running.
“Companies want to know,” Smith said. “The market is going crazy because it can’t get good information.”
Day to day, the stock market has no impact on the economy. But when it falls hard, consumers and companies alike can get spooked.
“They might stop buying cars,” Smith said. “They might stop buying houses. Companies might stop building up, they might start laying people off.”
Fears like that can become reality, he said. “The danger is in creating a self-fulfilling prophecy.”
Stock price change since September
Home Depot: -24 percent
Coca-Cola: 2 percent
Equifax: -32 percent
UPS: -21 percent
Delta Air Lines: -17 percent
SunTrust: -32 percent
Southern Company: 2 percent
Source: New York Stock Exchange, Yahoo Finance, staff research
For individuals: Tens of millions of Americans — not just the wealthy — are dependent on stocks, either through personal portfolios or retirement plans.
For companies: Many firms raise money by issuing stock or as currency to make acquisitions.
For all: Rising stocks tend to make people feel wealthier, so they spend more. Falling stocks do the opposite.