States were again unable to reach consensus on the text of a plastics treaty during negotiations in Geneva in 2025. The majority of states stood firm against petrochemical interests and demanded a “high-ambition” treaty with binding global obligations across the full life cycle of plastics. What these states specifically support, however, varies considerably, as does the strength of their commitment. The case of South Korea offers insights into how changes in political leadership, industry lobbying, shifting narratives and competing foreign policy goals can shape the nature of ambition. Early in the negotiations, South Korea called for ambitious measures and was chosen to host the final round of talks set for late 2024. Yet, this did not translate into meaningful action or strong advocacy in later stages. Some South Korean policymakers may have been sincerely committed to global controls. South Korea’s early signaling of high ambition, however, was primarily motivated by strategic calculations to influence the treaty and become a “global pivotal state.” Its support for ambition, moreover, grew increasingly ambiguous as leadership changed and as states describing themselves as “ambitious” pushed for binding controls on plastics production and supply. South Korea’s foreign policy strategy, we further argue, failed to enhance the country’s diplomatic standing, as its ambiguous ambition came to light, and as industry recalcitrance, bureaucratic infighting and political turmoil undermined its capacity for effective leadership.