Getting it be not sure happiness losing it be not sure pain.

得到的不一定幸福，失去的不一定心痛。

59-a youngster who does not know what he is good at will be not sure what he is good for.

一个不懂得自己精通什么的青年不会确切地知道他的价值所在。

I'm not sure there might be additional things that international students have to do like additional tests.

我不确定国际学生是否需要做额外的事情，比如额外的考试。

She had not known him long enough to be sure.

她认识他的时间还不够长，还不能肯定。

The idea "happiness", to be sure, will not sit still for easy definition.

可以肯定的是，“幸福”这个概念很难定义。