The increasing number of people living with chronic illnesses is an important healthcare issue for clinical and economic reasons. Fostering patients' self-management and responsibility for their care appears to be a strategy for promoting patients' quality of life over time. In this context, patients are asked to actively identify challenges in their illness and actively manage their health (i.e., self-management). However, involving patients in their health management is not free from psychological factors. For example, personality traits can facilitate or hinder the effective implementation of self-management within cancer patients while also impacting patient engagement, commitment to treatments, and decision-making processes about health. In this commentary, we try to shed light on the "dark side" of self-management. The term "dark side" is related to the absence of knowledge, comparable to the dark hemisphere of the Moon, which is not visible from the Earth and so poorly understood. Specifically, this commentary aims to describe the unexplored aspects and unsolved issues related to self-management, exploring the side not visible to Earth-bound observers related to the possible role of personality in the promotion of self-management in people with a history of cancer. Attention to personality traits may help promote better self-management for cancer patients and guarantee a higher quality of life, despite their chronic condition.