Which error should we try to avoid by having buffers? Central banking is like that. For all we know, we may not need our forex [foreign exchange] reserves. For all we know, our forex reserves may be much larger than we really need. But since we do not know, we would have to build reserves and prepare for the worst.
My favorite example is in the Bible, which is seven fat cows and seven lean cows. That was the dream of Joseph. Of course, that was just a saying. The business cycle can be as long as 14 years. Therefore, your needs could be bigger.