"...don't do to others what you wouldn't like done to yourself." [by Grondmaster]
There is a book, called "100 ways to make your self and your life miserable". One of the ways is to choose goal in life, that can not be accomplished.
I wish to make others happy or at least not to make them unhappy (if there is such a word). Generally I have a dream to make the world better. But since "better" is a relative characteristic and depends on what you compare with, someday (at the end of my days) I will probably find that the fact of me living on this earth made the world better someway.