He was treated badly? ! - I know. But...we have to be on our guard.

他还受了委屈？！-我明白，但我们得小心。

We can never be on our guard against all possible dangers.

我们永远无法对所有可能的危险保持警惕。

A police spokesman said that this was the third bomb scare within a week and that we should all be on our guard.

警局发言人说，这已经是本周的第三起炸弹威胁。因此，所有警员都得全员在岗，严阵以待。

The Tao is (like) the emptiness of a vessel; and in our employment of it we must be on our guard against all fulness.

道冲而用之或不盈。