* The destructive nature of self-deception and denial: Tracy's avoidance of responsibility, his constant rationalizations, and his inability to face the consequences of his actions ultimately lead to his downfall. The novel powerfully illustrates how clinging to illusions can prevent personal growth and happiness.
* The cyclical nature of addiction and self-destruction: Tracy's pattern of relapse highlights the difficulty of breaking free from destructive habits and the ease with which one can fall back into old patterns. This suggests a powerful cyclical element to many personal struggles.
* The limitations of romantic love as a solution to deeper problems: Tracy's relationships, especially with his wife, are fraught with tension and misunderstanding. The novel suggests that relying on romantic love to solve fundamental personal issues is often futile. It's not a cure-all for deeper unhappiness.
* The pervasiveness of loneliness and alienation in modern society: Yates portrays a world where characters struggle to connect meaningfully with each other, leading to feelings of isolation and despair. This resonates with many readers' experiences.
* The inevitability of disappointment and the difficulty of achieving lasting happiness: The novel's ending underscores the sense that life rarely unfolds as we plan, and that true, lasting happiness might be an elusive goal.
In short, "Criss Cross" doesn't offer simplistic answers or easy morality tales. Instead, it presents a realistic and often bleak portrayal of human nature, leaving the reader to contemplate the complexities of life and the challenges of self-awareness and personal responsibility. The "lesson" is less a prescriptive statement and more a deep reflection on the human condition.