You never know who or what might walk through the door.

VOA: standard.2010.07.06

To put it differently, in order to know what "Dogs" means, you never had to learn the word "Dogs."

换个说法,为了知道"狗狗们"的意思,你不需要去学"狗狗们"这个词

耶鲁公开课 - 心理学导论课程节选

just 'cause you will never know what you're going to get.

就因为你永远也不知道在那里会有什么。

圣莫妮卡和洛杉矶 - SpeakingMax英语口语达人

Now we will never know, and don't let anyone ever suggest to you that you will ever know, what Milton could possibly mean by this deliberately perplexing image of the two-handed engine at the door.

我们永远不会知道,弥尔顿在这句描写门边的双手引擎的,刻意的意象叠加里想要表达什么。

耶鲁公开课 - 弥尔顿课程节选