Perfect health, like perfect beauty, is a rare thing; and so, it seems, is perfect disease.
Although economists have studied the sensitivity of import and export volumes to changes in the exchange rate, there is still much uncertainty about just how much the dollar must change to bring about any given reduction in our trade deficit.
Short-story writing requires an exquisite sense of balance. Novelists, frankly, can get away with more. A novel can have a dull spot or two, because the reader has made a different commitment.