To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge.

To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge.

知道我们知道我们所知道的，知道我们不知道我们所不知道的，这就是真正的知识。

-- Nicolaus Copernicus 哥白尼