虽然不能预知未来，但了解一点历史也没有坏处。道琼斯指数自1946年以来有31次下跌10％，其中12次（约40％）开启20％以上跌幅。

Since 1946, there have been 31 instances of a 10% drop. But a 10% drop doesn’t necessarily lead to a 20% one (which denotes a bear market) — in fact, in just 12 of those 31 instances did a bear market eventually ensue.