来自《耶鲁大学开放课程：金融理论 第13集 第13集》

• 
  
  So economists for a long time
  经济学家们假设一切符合正太分布
• 
  
  assumed that everything was normally distributed,
  很久一段时间
• 
  
  but an implication, as I say,
  但是暗示着 正如我所说
• 
  
  of normal distribution is that
  正太分布中
• 
  
  it's very unlikely something extreme is going to happen,
  极端事件是不太可能发生的
• 
  
  because this thing goes down exponentially fast to 0,
  因为这样的事指数上趋近于0
• 
  
  so you're almost never going to see something way out here.
  所以你用正太分布基本能得到所有的东西
• 
  
  Yet we get these crashes fairly frequently.
  但是我们看到的破产概率上是公平的
• 
  
  Every 10,20, 30 years or something,
  每10 20 30年或其他
• 
  
  there's some gigantic outlier.
  会有很多异常值
• 
  
  So clearly things can't be normally distributed,
  所以清晰的事是正太分布给不出来的
• 
  
  and that's called fat tails.
  这叫肥尾现象