In 2011, during the scariest times for the euro zone, the country's safe-haven status turned the nation into an island of tranquility. Money poured into it from elsewhere in the euro zone as investors sought a safe place to park their cash.

Of course, with everyone wanting to have their money in Switzerland, the franc exploded in value. In early 2010 one franc was less than 0.7 euro. By the middle of 2011 the franc was nearly at parity against the euro, a massive move in a very short period.

Countries typically don't like it when their currencies zoom like that. The most obvious reason is that it's bad news for domestic exporters, whose goods become less competitive abroad. Switzerland is known for its high-value exports, such as watches and pharmaceuticals, so a surging currency isn't helpful. There are other reasons related to financial-system plumbing that create a problem for a country when a huge slug of foreign cash rushes in.

So in the summer of 2011, the Swiss National Bank announced a cap on the exchange rate between the euro and the franc. The euro wouldn't be allowed to weaken below 1.20 against the franc. The bank maintained the cap by printing francs on a regular basis to buy euros in the market to ensure that the currencies wouldn't breach that line. The cap held without a hiccup for more than three years.

So what happened today?

Without any hint that it was coming, the bank removed the cap, causing the franc to soar against other currencies.