Ha! Ha! Master AP, I think it is YOU make the situation even more complicated. I hope poster would not get even more confuse without understanding the logic behind your saying.
2014-02-12 02:12:05 補充：
I think, it is GOOD to know these, after all, my saying too simplified. Especially, your saying: 語言有時候應用雙重否定(甚至3重否定)來強調"否定 is a good point.
2014-02-12 07:16:48 補充：
To follow this "common sense," shall we exchange the position between answer and opinion?
2014-02-12 14:07:29 補充：
I like master Louis's answer. It is a good point to consider the use of "should", not "shall". Thanks a lot for pointing it out.