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個月的時間范圍內，推動股市的是投資者心理，偶爾還有危機。4月末，衡量投資者熱情的指標顯示，一波避險浪潮可能馬上就會出現。5月末，市場人氣、風險愛好以及其它類似指標走向另一個極端，顯示風險很可能上升。股市下跌前一刻，投資者滿懷激情地給風險定價；下跌結束時，對風險的定價則畏手畏腳。引用沃倫?巴菲特(Warren Buffett)的話：“當其他人貪婪時，我們應謹小慎微，當其他人謹小慎微時，我們應該貪婪。”