"Imagine, as is in fact the case, that maple sugar is three times as expensive on Tau Ceti as it is on Barrayar. This is stable because it takes a lot of hassle to get maple sugar from Barrayar to Tau Ceti, and the people involved in that hassle mark it up. Now imagine that," she pats the bar, "the economies of Tau Ceti and Barrayar are right next to each other, and you have an intermediary who doesn't cheat you at the currency exchange, and further that there are several trillion other economies also right next to each other, and quintupling your money starts to sound trivial."