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.

正如我们所知，有已知的已知。有些事情我们知道我们知道。我们也知道有已知的未知。也就是说，我们知道有些事情我们不知道。但也有未知的未知，那些我们不知道我们不知道的。