A study conducted among 338 mothers in Hangzhou, China, explored breastfeeding self-efficacy within the first six months postpartum, framed by Life Course Theory. The research, carried out from May to August 2023, utilized convenience sampling and included questionnaires on general information, breastfeeding knowledge, and the Breastfeeding Self-Efficacy Scale. Findings indicated a moderate overall self-efficacy score, averaging 111.32. Key factors influencing self-efficacy were identified as the primary feeding methods and breastfeeding knowledge. Notably, a counterintuitive relationship between knowledge and efficacy was observed, suggesting that increased knowledge did not always correlate with higher self-efficacy, potentially linked to impostor syndrome among new mothers. The study emphasizes the importance of tailored interventions to enhance breastfeeding self-efficacy and calls for further investigation into the identified knowledge-efficacy relationship.