How Do You Work It Out?

I've taken so many stabs at finding a 'dream' future career, but I just don't know. I wish I did.  I -really- wish I did.  They you're supposed to just 'know' when you've landed on the right one, but I just don't know.  How do you work it out?  How do you separate all the "maybes" and land on the 'yes!'? 

What is it that I can do to help differentiate between what would be nice to do and what I really want to do?  How do I discover my dream job?

Edit to add:  *smiles*  Now I know.  A dream job is not one without potential problems or dislikes:  It is one in which is suitable to such an extent that the unfortunate points about it can be outweighed by its greater positive aspects.  

( I think I've found mine.  ;-D )