Purpose: Patients with gastric cancer experience several challenges in regaining self-efficacy, including postoperative gastric dysfunction and psychosocial problems, after undergoing gastrectomy. This study aimed to describe the process of regaining self-efficacy in cancer survivors who underwent gastrectomy. Methods: This study enrolled adults, employed a modified grounded theory approach, and targeted participants by theoretical sampling. Data were collected via semi-structured interviews and analyzed by qualitative and inductive methods. Results: The participants included 10 post-gastrectomy patients with gastric cancer. The analysis yielded 28 concepts, eight categories, and four core categories. Regaining self-efficacy in cancer survivors began with “Facing gastric cancer and surgery.” After a period of being “At the mercy of gastrectomy and eating habits,” it changed to “Reclaiming life while accepting the loss of gastric function” through trial-and-error, and finally reached the stage of “Aiming for a better future than that before gastric cancer” after a long period. Conclusion Despite a crisis and repeated trial-and-error circumstances that could change abruptly, the patients demonstrated a flexible and resilient attitude in regaining self-efficacy. This study presented a time axis of the difficult process of regaining self-efficacy and explained the stages at which nursing intervention becomes important.