Equity markets are driven by investor psychology and, occasionally, shocks over one- to three-month time horizons. In late April, measures of investor exuberance indicated that a wave of risk aversion was likely and imminent. By late May, sentiment, risk appetite and other similar indicators had swung to the opposite extreme, signalling a high likelihood of a rally in risk. Immediately before the sell-off, investors priced risk exuberantly. At the end of it, risk was priced fearfully. To quote Warren Buffett: "We should be fearful when others are greedy and greedy when they are fearful."
在1到3个月的时间范围内，推动股市的是投资者心理，偶尔还有危机。4月末，衡量投资者热情的指标显示，一波避险浪潮可能马上就会出现。5月末，市场人气、风险爱好以及其它类似指标走向另一个极端，显示风险很可能上升。股市下跌前一刻，投资者满怀激情地给风险定价；下跌结束时，对风险的定价则畏手畏脚。引用沃伦•巴菲特(Warren Buffett)的话：“当其他人贪婪时，我们应谨小慎微，当其他人谨小慎微时，我们应该贪婪。”