Fun fact of the day: Multiple numeraires can make trading non-zero-sum.
Let's say we have currencies A and B tied to countries with citizens a and b caring about their holdings in their respective currencies.
A and B are at parity, will move to 2:1, one will double, the other halve, 50/50 as to which.
a invests in B, expecting a return of 0.5*2 + 0.5*0.5 = 1.25.
b takes the other side of the trade, and has the same expected return!
Magic! ;)
(Sometimes I miss finance.)
I assume some process will flip a fair coin to choose which of {A, B} will go up and which will go down.
In that case it seems to me that holding any combination of A and B is equally good. I don't see how this could be an example for principles intended to be used to choose an investment, given that there is no meaningful choice to be made here.
@robryk I think you're unusual, then, in that most people tend to think of how rich they are in terms of either the currency where they live, or maybe a major international currency.