美国前国防部长拉姆斯菲尔德谈伊拉克是否有大规模杀伤武器时说的。

奇迹之星

Reports that say that something hasn't happened are always interesting to me ， because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns: the ones we don't know we don't know."
      我一向对尚未发生的事情的有关报道感兴趣， 因为据我们所知，有‘已知的已知’，有些事，我们知道我们知道；我们也知道，有‘已知的未知’，也就是说，有些事，我们现在知道我们不知道。但是，同样存在‘未知的未知’——有些事，我们不知道我们不知道。”