When the financial crisis broke in August 2007, David Viniar, chief financial officer of Goldman Sachs, famously commented that 25-standard deviation events had occurred on several successive days. If you marked your position to market every day for a million years, there would still be a less than one in a million chance of experiencing a 25-standard deviation event. None had occurred. What had happened was that the models Goldman used to manage risk failed to describe the world in which it operated.
2007年8月金融危机爆发伊始，高盛(Goldman Sachs)首席财务官戴维•维尼亚(David Viniar)曾发表过一个著名的评论：标准差为25的事件连续几天出现。假如你在100万年的时间里每天都按市值计算自己的头寸，遇到一次标准差为25的事件的几率仍不到一百万分之一。这种情况从未出现过。问题出在高盛的风险管理模型未能正确描述自己所处的世界。
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