Despite the potential for personalized learning, e-learning courses often suffer from low completion rates. In order to address this issue, we propose and empirically test a theoretical mechanism that examines how gamification can enhance the completion rate in adaptive learning courses by promoting a more positive behavioral response and attitude among students. To identify causal effects, we employ a quasi-experimental design with a time-discontinuity in treatment attribution. Our study involves a sample of 6592 adults who participated in a Belgian financial education platform. The effect sizes were estimated using non-parametric survival analysis. Our findings indicate that gamification led to a 5.7% increase in the number of questions answered and a 1.6 percentage point rise in the completion rate. These effects were particularly pronounced among younger individuals, single adults, and in relation to socioeconomic status questions used in the personalization survey. However, gamification did not significantly impact the completion rate for decision-making questions. By demonstrating that gamification serves as a causal mechanism for enhancing completion rates in adaptive learning courses, our study contributes to the underlying e-learning theory. Specifically, we highlight the role of psychological factors, such as improved behavior and attitude, which are particularly relevant during personalization surveys.