Consumers are increasingly using technologies such as wearables or mobile apps to achieve their self-improvement goals. Such technologies often contain features that enable social interdependence among users (competition or cooperation) to support them in improving their engagement, performance, and well-being (life satisfaction and personal growth). However, the critical question remains: does competition or cooperation best serve users in attaining these self-improvement goals? Evidence from an online experiment and a field study reveals that competition is more effective in driving performance and personal growth, while cooperation is superior in terms of behavioral engagement and life satisfaction. Furthermore, the results indicate that the effects are mediated by strive for success and fear of failure, two counteracting psychological processes. While competition is the stronger trigger for both pathways, downstream effects vary depending on the self-improvement goal considered. This research thus provides insights into whether and how users can best realize their self-improvement goals using technologies that include social features.