The purpose of the study is to explore the structural relationships among second language (L2) proficiency and the constructs of L2 learners' resilience, motivation, and demotivation. A total of 869 undergraduate students in South Korea participated in the study. The data were analyzed by means of factor analysis, correlations, and structural equation modeling (SEM). The factor analysis identified seven resilience factors (life satisfaction, sociability, communicative efficacy, self-composure, strategic competence, metacognitive adaptation, and realistic optimism), six motivation factors (ought-to L2 self, ideal L2 self, instrumental motivation, parental support, academic motivation, awareness of importance), and six demotivation factors (negative perception of English-speaking countries, compulsory EFL learning, perceived inappropriateness of textbooks or tasks, low self-esteem, unsupportive learning environment, unsupportive teachers). The SEM corroborated that resilience, L2 learning motivation, and L2 learning demotivation contribute to L2 proficiency. L2 learning demotivation had more explanatory power for L2 proficiency than did L2 learning motivation. Resilience had both a direct and an indirect effect on L2 proficiency via L2 learning demotivation. The findings suggest that teachers should equip learners with strategies to manage adversity in L2 learning.