Certainly the short story has always been more flexible and open to experiment than the novel. Short-story writers always have been subject at the same time to both a stricter technical discipline and a wider freedom than the novelist. Short-story writers have known—and solved by nature of their choice of form—what novelists seem to have discovered in despair only now: the strongest convention of the novel, prolonged coherence of tone, to which even the most experimental of novels must conform unless it is to fall apart, is false to the nature of whatever can be grasped of human reality. How shall I put it? Each of us has a thousand lives and a novel gives a character only one. For the sake of the form. The novelist may juggle about with chronology and throw narrative overboard; all the time his characters have the reader by the hand, there is a consistency of relationship throughout the experience that cannot and does not convey the quality of human life, where contact is more like the flash of fireflies, in and out, now here, now there, in darkness. Short-story writers see by the light of the flash; theirs is the art of the only thing one can be sure of—the present moment. Ideally, they have learned to do without explanation of what went before, and what happens beyond this point. How the characters will appear, think, behave, comprehend, tomorrow or at any other time in their lives, is irrelevant. A discrete moment of truth is aimed at—not the moment of truth, because the short story doesn’t deal in cumulatives.
From Nadine Gordimer, “The Flash of Fireflies” in Charles E. May, ed., Short Story Theories (1976).