What, then, can strike a balance between the opposing forces operating on the euro-dollar exchange rate? No one can say for sure, but one thing is certain: Whereas the profits from playing transatlantic interest-rate differentials may run to 1% or 2% per year, investors can easily lose that amount in a single day – or even an hour – by buying the wrong currency when the trend turns. As we know from decades of Japanese and Swiss experience, selling a low-interest-rate currency simply to chase higher US yields is often a costly mistake.