http://www.ft.com/cms/s/0/2a1afcee-42e0-11dd-81d0-0000779fd2ac.html
Pay attention to the last paragraph.
FX pairs are like a partially used tube of toothpaste ,squeeze one end , the toothpast moves to the other, it can't get out of the tube, it just moves back and forth as one of the ends...