He never knows when to stop.

他不知道什么时候该停。

youdao

The secret strategy for managing a mind blank so that your audience never knows.

当你大脑一片空白时，也不会让听众觉察的秘密解决方案

youdao

When people change shifts, the brain never knows when it's supposed to be asleep, so this affects how people function.

当人们换班时，大脑不知道什么时候该睡觉，这样就会影响人们身体机能的运转。

youdao

Can you lead the tracker away from here? No, Edward.James knows you would never leave Bella.

VOA: standard.other

We'll never find Truth in her entirety, at least not until the Second Coming, and who knows when that will be?

我们永远找不到完整的真理，至少在第二次到来之前不能，谁知道那将是什么时候呢？

耶鲁公开课 - 弥尔顿课程节选

Should we say of somebody who's fainted or knows that they're subject to fainting spells, they never actually believe that they pass out?

我们该说那些昏倒了,或者是中了昏迷魔法的人，不会相信自己昏倒了吗？

耶鲁公开课 - 死亡课程节选

But then again, one never knows the twists and turns that boxing can take.

WSJ: Bradley Wins Controversial Decision Over Pacquiao

Another significant difference: A person whose email is inspected this way often never knows a search was conducted.

WSJ: Court Order Seeks Email Data of WikiLeaks Volunteer Jacob Appelbaum

One never knows when one will need that but one knows it will.

FORBES: (mini)Review: The NY Times' Mapping America Project