A country can only choose two of the following three properties for its currency: - A stable exchange rate (with a fixed peg) - Independent monetary policy (setting your own interest rates to fight inflation / recession) - Free capital flow (Letting money move in and out of the country freely) The Swiss Franc shock of 2015 seems to have been the result of Switzerland trying to get all three. The gravity of the Euro and the Dollar eventually became too strong and they couldn't keep printing money by the billions. When they couldn't keep up, the exchange rate moved $30\%$ in minutes.