According to Leslie, those who ridiculed former Defense Secretary Donald Rumsfeld for his 2002 remark that we have to be wary of the unknown unknowns were mistaken.
2017年12月四级真题（第二套）阅读 Section B
柯林斯高阶英汉双解学习词典释义
ADJ
不知道的；不了解的；未知的
If something is unknown to you, you have no knowledge of it.