Keynes taught that a country can either have external stability or internal stability, but not both at the same time. External stability is constant exchange rates. Internal stability is normal growth, not distorted by exchange rate pegs. Maintaining external stability requires adjusting interest rates to keep capital flows from changing the exchange rate too much. Maintaining internal stability requires countercyclical interest rate policy: lower in recessions, higher in booms. Hence, the conflict.
In practice, every commodity peg has been successfully attacked and so have many exchange rate pegs. The only pegs that have been stable (with a notable exception in Argentina) are currency pegs, normally implemented by an exchange board that trades currency to maintain the exchange rate within a preset band. The main problem with this is that the country doing the peggings is importing the pegged country's macroeconomic policy. Argentina has shown that the attempt to enforce internal discipline can fail, too, leading to policy collapse.