That means you can give someone advice but you cannot force him to do something he does not want to do.

VOA: special.2009.07.12

You cannot just tell the computer to enhance that or can you clean that up and then magically use zoom in not only on the image but also on the reflection of the victim in someone's eyeball.

你不能直接要求计算机增强,这张图片或者修复它,然后期待计算机很神奇地放大图片,以及死者的眼珠的反光。

哈佛公开课 - 计算机科学课程节选

Now, it's not obvious but it is true that you cannot add to this anymore.

虽然不是很明显,但你确实无法再往后面加什么东西了

耶鲁公开课 - 基础物理课程节选

But, she adds, "just because you cannot do everything does not mean you should do nothing"--not exactly a prescription for when to go in and when to stay out.

CNN: Blunt But Flexible

Thatcher asserted, also knows that if you do not provide you cannot be certain that anyone else will.

WSJ: What Would Margaret Thatcher Do?

Frankly, if you cannot do it properly you should not be doing it at all.

BBC: From the editor's desktop: Your response