In a world without massive intervention a currency should rise when the economic prospects rise and fall when they fall. That would mean the dollar would rise with stocks and fall with stocks as bonds would rise in economic uncertainty or decline. Now things are backward because stocks are looking for more Fed/government intervention. Thus, falling economic strength leads to a weaker dollar as it should, but even more so because weakening economic data can mean more Fed intervention and thus a weaker dollar (devaluing the currency) but stronger stock prices thanks to the increase in liquidity. So half of the equation changes when there is intervention. It then becomes a race: can you earn more money in stocks than you lose in the value of your dollars. If hyperinflation hits, well, you lose at that game.