The Western Australian mining sector stands at a critical regulatory juncture. While the industry has continued progress on engineering controls for physical hazards, the rising prevalence of psychosocial risks coupled with the new Code of Practice obligations (AICD and KWM, 2025) exposes a significant gap in our safety architecture. Traditional ‘Swiss Cheese’ models, designed for tangible hazards, often fail to contain invisible stressors such as production pressure, fatigue, and role ambiguity (Stuckey-Clarke et al, 2026). When organisational systems falter, the frontline worker’s psychological state and personal capacities become the ‘last line of defence’ against an incident. This research proposes a reconceptualisation of Psychological Capital (PsyCap), comprising Hope, Self-Efficacy, Resilience, and Optimism (HERO), not merely as a well-being metric, but as a quantifiable safety control. Furthermore it challenges the industry’s reliance on generic resilience training. Instead, it posits that without a supportive Psychosocial Safety Climate (PSC) and high quality supervisor relationships, individual resilience can become a liability leading worker to ‘tough out’ unsafe conditions (the ‘Dark Side’ of PsyCap). We hope to offer Mining leaders a new perspective in that PsyCap is a malleable, measurable state that can be developed and audited. By treating human psychological factors with the same rigour as engineering controls, the mining sector can move from reactive mental health support to proactive psychosocial risk management, ensuring the ‘last line of defence’ is robust, supported, and sustainable.