Quote from lundy:
first, a person would have to know what the result of the event would be. Theres only 2 choices, up or down, and neither is obvious.
A bombing could rally the dollar for all u know.
Maybe so, but if you knew before hand that the BoJ was going to be buying large quantities of Yen at a certain time, there would be an obvious trade there. It might not be 100% certain to make the yen rise, but you definitely have an edge knowing that ahead of time and going long Yen.