How could it work if say... we accept the Multiverse theory? That's where I go into a tale-spin cycle.
If a fortuneteller were to look at our lives from another angle, they might see the inevitable. An aerial view, if you will. They could know your relationship isn't going to last because from up there, they can see he's already cheating.
But what about The Secret?
What if tapping into a superconscious gives the fortuneteller information from collective knowledge. For example, he's already thinking about leaving you, but he hasn't said anything. Or maybe the fortuneteller is looking into your past and picking out familiar patterns. All of these things involve perspective alone. What if the fortuneteller can't change her perspective (she is only human after all) but she can contact someone who does ...like a ghost...or a djinn. Yes, djinn are supposed to live in a parallel universe, so that theory works like magic!
Why is it that we accept angels, ghosts and demons without a second thought, but seeing the future needed an explanation?