The Impossible Trinity

While reading O Canada, an article by Paul Krugman on Robert Mundell's Nobel Prize I saw the following bit of brilliance:

Later Mundell would broaden this initial insight by proposing the concept of the "impossible trinity"; free capital movement, a fixed exchange rate, and an effective monetary policy. The point is that you can't have it all: A country must pick two out of three. It can fix its exchange rate without emasculating its central bank, but only by maintaining controls on capital flows (like China today); it can leave capital movement free but retain monetary autonomy, but only by letting the exchange rate fluctuate (like Britain--or Canada); or it can choose to leave capital free and stabilize the currency, but only by abandoning any ability to adjust interest rates to fight inflation or recession (like Argentina today, or for that matter most of Europe).

When looking at the Wikipedia article for said 'Impossible Trinity' I found it to reference exactly that quote from this same article. Well, it really is an excellent summary of a very interesting idea.