The financial markets run on data and numbers. But they are also driven by emotion, even in this age of computer trading.
Emotion was on display in the final hours of trading last week as stocks on Wall Street plunged more than 3 percent.
There was anxiety, confusion and some traders admitted there was even a hint of panic.
The Dow Jones Industrial Average fell over 500 points and is now 10 percent below its May peak. That means it is officially in correction territory.
The broader S&P500 fell 3.2 percent. That is its biggest one day fall in almost four years.
The spur for the sell-off was weak Chinese manufacturing data and another drop in the Chinese share market (down 4 percent). Chinese factory production slowed at its fastest rate in almost six-and-a-half years, as imports and exports fell.
That added to the existing concern about slowing global growth and falling commodity prices.
On top of that many investors have felt for some time that US stock valuations had got ahead of themselves and a correction was overdue.
US markets typically correct once or twice a year. But there had not been a correction since late 2011.
All this was enough to spark a sell-off.
The S&P500 lost 5.8 percent for the week. That was its biggest weekly fall since September 2011. British shares lost 5.5 percent for the week, European shares fell 6.5 percent and Australian shares lost 2.3 percent.
The New Zealand market gained ground however. It was up 1 percent for the week and is only 3 percent down from its peak (although the New Zealand index includes dividends - most markets do not).
Oil prices had a very bad day. At one point during trading, West Texas Crude fell below US$40 a barrel.
It finished down 2 percent at US$40.45. That is its lowest level in six years and five months. It was down 6 percent for the week.
European Brent fell to its lowest level since March 2009, at $45.10 a barrel. It closed at $45.46.
US oil prices have fallen for eight weeks in a row. That is the commodity's longest losing streak in 29 years.
August is a notoriously volatile month for stocks.
The VIX index measures volatility in the markets (specifically options on the S&P500 index). It leapt 46 percent on Friday to 28, its highest level since December 2011.
The VIX has risen 131 percent this month.
US stocks have fallen in three of the previous five Augusts.
However the perception that August is bad for stocks is wrong. US markets have risen in 10 of the last 15 Augusts.
The New Zealand market will begin trading at 10am local time. But the focus will be on the Asian markets this afternoon, particularly China.
US investors would not typically focus on a market largely made up of individual investors. But they will want to see how the Chinese government might react and whether it will attempt to intervene again.
The country's official news agency reports that China plans to allow its main state pension fund to invest in the stock market for the first time.
It will be able to invest up to 30 percent of its assets in domestic shares.
The Shanghai Composite is Index lost 12 percent last week and is down more than 30 percent from its peak.
The Middle Eastern markets were the first to start trading this week. They trade on a Sunday (the early hours of Monday New Zealand time) and were sold off sharply.
The Dubai Financial Market fell almost 7 percent, Saudi Arabian stocks were down 7 percent and the major indexes in Tel Aviv fell over 4 percent.
The New Zealand dollar appeared to have been a beneficiary of the uncertainty.
It gained around 2 percent last week against most of the major currencies, except the euro.
The kiwi was trading at 66.58 US cents at 8am this morning.
That was down from 66.94 at 6am. But it is higher than 66.30 cents on Friday morning and 65.40 cents a week ago.
The kiwi is 91.35 Australian cents, compared to 90.34 Australian cents on Friday and 88.64 last Monday.
But the kiwi is down against the euro. It is trading at 58.50 euro cents compared to 59.12 on Friday.
The dollar is trading at 42.46 British pence, compared to 42.26 pence on Friday.
It is 81.04 yen, compared to 81.83 on Friday.