对某人而言，这依然是个迷。

It is still a mystery to sb.

对某人而言，做某事是可能的；

It is likely for sb. to do sth.

对某人而言，做某事是可能的；

It is possible/probable for sb. to do sth.

对世界而言你是一个人，但对某人而言你是一个世界。

You may only be a person in this world, but for someone yiu are the world.

对某人而言是有困难的，看太多的电视对眼睛有害。

It's difficult for somebody watching TV too much harmful to his or her eyes.