How does O'Neill use symbolism in the play, Long Day’s Journey into Night?

O'Neill, within the realistic limits of his drama, uses symbolism very effectively. Of fundamental significance is the fog. It serves first as a mood enhancing but wholly natural phenomenon. At the beginning of the play, the fog of the night before has lifted, and the optimism of the Tyrone family is reflected in the day's early brightness. But by dinner time in Act Three, the fog has again rolled in, its presence announced by a foghorn "moaning like a mournful whale in labor." Its return suits the encroaching sense of futility and isolation of each of the main characters, particularly Mary. It is she who asks why the "fog makes everything sound so sad and lost."