Source: Economist -

GENERAL ARGUMENT: If two variables have been in a certain relation for a long time, the fact that such a relation does not seem to hold anymore can be a reason of puzzlement (and must be explained).


Not shown in the chart (but part of the argument) -"In the first 3 months of this year, the currency got stuck in an unusual narrow range.... This puzzled currency-watchers. Afterall, there are plenty of good reasons why the dollar ought to rise this year. "

Shown in the chart -"The first is that current-account imbalances are shrinking... The yen/dollar exchange rate tends to move broadly in line with the two countries' relative current-account positions (see chart)"