Objective To identify factors contributing to ego-depletion in patients with type 2 diabetes mellitus (T2DM) and to provide reference for targeted interventions. Methods Using phenomenological qualitative design, 17 T2DM patients were purposively selected for semi-structured in-depth interviews conducted by trained researchers. Data were analyzed via Colaizzi′s seven-step method to extract themes. Results Two main themes and seven sub-themes emerged:direct triggers:negative affect, decision-making dilemmas, impulse restraint, and competitive tasks; and indirect contributors:lack of motivation, insufficient support, and low self-efficacy. Conclusion Direct triggers induce acute exhaustion of self-regulatory resources, while indirect contributors exacerbate long-term vulnerability through compromised coping capacity. Their synergistic interaction accelerates ego-depletion progression. Nursing interventions should address these mechanisms through tailored strategies to enhance self-regulation and mitigate depletion-related adverse outcomes.