AlthoughEugene O'Neill's Long Day's Journey into Night may be depressing and emotionally draining, it demonstrates a number of important elements of family relationship theory, including the interactions between siblings, spouses and their lives over time; combined, these interactions draw a picture of the family as the container and sustainer of life. The play advances the theme that, within the context of the family, the ghost of the past plays itself out in the present. The play also demonstrates that families are often centers of conflict and contradiction.