This study examined the teaching motivation and demotivation of private English instructors in South Korea, a sector influenced by market pressures, parental expectations, and organizational instability. While extensive research has focused on public school teachers, the motivational dynamics of private instructors remain underexplored, despite their significant role in the Korean education system. Through semi-structured interviews with twelve instructors at various school levels and job positions, the study utilized qualitative thematic analysis to uncover key motivational and demotivational factors. The findings indicated that instructors’ motivation was driven by student achievement, relational affirmation, and professional recognition, while demotivation stemmed from parental pressure, limited autonomy, lack of collaboration, and systemic instability. Notably, motivation and demotivation were not isolated states but interdependent processes influenced by the fulfillment or frustration of core needs. This study contributes to existing literature by contextualizing established frameworks such as Self-Determination Theory, the Job Demands–Resources model, and organizational justice within the private education sector. By highlighting the fragile nature of motivation and the dual role of structural conditions as both assets and challenges, the findings provide insights for enhancing teacher wellbeing and instructional quality in market-driven educational environments.