Understanding what drives people to maintain essential health behaviors during global crises could reshape how public health systems prepare for future pandemics. The dramatic decline in cancer screening during COVID-19 represented a potential time bomb for delayed diagnoses and worse outcomes, making the psychology behind screening decisions critically important for health policy. A four-month longitudinal study of 270 Japanese adults revealed a striking paradox in how pandemic fear affects cancer screening behavior. While initial COVID-19 anxiety actually increased people's stated intentions to undergo gastric cancer screening, this same fear ultimately prevented them from following through with actual screening appointments months later. The research identified health literacy, perceived cancer susceptibility, and environmental cues as the strongest predictors of both screening intentions and actual behavior. Participants with higher health literacy were more likely to recognize the continued importance of cancer prevention despite pandemic risks. Implementation intentions—specific plans about when and where to get screened—served as a crucial bridge between wanting to get screened and actually doing it. This finding illuminates a critical gap in pandemic health messaging that focused heavily on infection control while potentially undermining other essential preventive care. The study's focus on gastric cancer is particularly relevant given Asia's elevated rates and the procedure's invasive nature, which likely heightened COVID-19 transmission concerns. The research suggests that effective pandemic preparedness requires nuanced messaging that acknowledges legitimate infection fears while reinforcing the ongoing necessity of cancer screening. Future public health strategies might benefit from emphasizing specific implementation planning and leveraging health literacy education rather than relying solely on fear-based motivation, which appears to create short-term intention spikes but long-term behavioral paralysis.