This chapter confronts the reality of moral evil by examining its two key dimensions: vice and sin. It defines vice as a corrupting habit that disposes one toward evil, often stemming from the Capital Sins like pride and envy, which are rooted in disordered self-love. Sin is presented as a specific act—a thought, word, or deed—that turns away from God and His eternal law. A central focus is the crucial distinction between mortal sin, a grave offense that destroys the life of grace in the soul, and venial sin, which wounds our relationship with God but does not sever it. The chapter also clarifies the nature of original sin as the inherited state of wounded human nature that inclines us toward sin. Finally, these theological concepts are connected to contemporary psychological insights on addiction and moral failure, showing that understanding our capacity for sin is essential for appreciating our profound need for divine grace and redemption.