rule the motives which have prompted States to accept it have varied from case to case. It could not be otherwise. At all events, to postulate that all States, even those which initiate a given practice, believe themselves to be acting under a legal obligation is to resort to a fiction, and in fact to deny the possibility of developing such rules."

As difficult as it can be to prove why an actor did act in a certain way, it is exponentially more difficult to prove why it did not act. For this reason, the necessity of demonstrating that