The difference between winning and losing in the FX market is usually just a matter of luck. To a first approximation, floating exchange rates seem to follow a random walk (see here). But the trade I'm describing here is one I think we should have expected to pay off for reasons beyond pure luck. That is, there is a pretty sensible theory of currency crises that might have guided our investment strategy in the present context. In particular, I'm thinking of Paul Krugman's (1979) model, which he describes here.
The basic idea is as follows. Suppose that a central bank wants to peg its currency relative to some other currency. Suppose that it does so unilaterally. The success of the peg will depend critically on its perceived credibility. This credibility may depend on, among other things, the amount of foreign reserves held by our intrepid central bank. To defend the peg, the central bank must stand ready to buy its own currency on the FX market, which it does so by selling off its stock of foreign reserves.
A unilateral peg of this sort is just ripe for speculation. The two most likely outcome in this case are (1) the peg holds or (2) the peg fails (the domestic currency depreciates). The trade in this case is to go short on the pegging bank's currency and long in the foreign currency. A speculator either breaks even if (1) or wins if (2). It's a can't lose proposition (but please don't try this at home kids). Rational speculators, recognizing the opportunity, start shorting the pegged currency. If they do so en masse, our little central bank will soon run out of reserves and be forced to abandon the peg--a self-fulfilling prophecy.
I didn't spot this in the case of the SNB because, well, Switzerland is not a banana republic--the Swiss Franc is considered a safe-haven security. And the SNB was pegging because it was worried about currency appreciation--not the usual concerns about excess volatility or depreciation. Of course, there was never any danger of the SNB running out of reserves--they can print all the Francs they want! So what was the danger?
Central bankers are by nature a highly conservative bunch. They become uncomfortable with things that are unfamiliar. Like historically huge balance sheets, for example. With an ECB QE policy on the horizon, there was the prospect of EUR for CHF conversions proceeding at an even more rapid rate--leading to a very, very large SNB balance sheet. My thought is this: we should have guessed that the SNB would have at some point in this process lost its nerve and abandoned the peg, allowing their currency to appreciate And if it didn't lose its nerve, the peg would have been maintained, so we would not have lost on the other likely outcome of my proposed bet.
As for the SNB abandoning its peg, especially the way it did, well, it seems rather odd to me. It would have made sense if one thought that EUR inflation was likely to take off. But all the worry at present is directed toward the prospect of EUR deflation. Yes, that's right, the SNB is stocking up on a currency whose purchasing power is projected to increase. And as for being concerned about EUR inflation because of QE, it seems unlikely to me that the ECB wouldn't be willing and able to defend its low inflation target.
In short, I think the SNB could have let it's balance sheet grow much larger without any significant economic repercussions. Instead, by removing the peg as they did, they suffered a huge and needless capital loss on their EUR assets. Strange move? But how can we argue against the past success of Swiss bankers?
On the plus side, I suppose we can no longer claim the Swiss to be boring!