Duolingo has replaced its hearts system with an energy mechanic to focus on rewarding correct answers instead of punishing mistakes.Under the new system, users start with 25 energy units and can earn bonus energy randomly for correct answers.The shift from loss aversion to an investment model transforms the psychological experience of learning.The new system incorporates variable reward schedules, similar to slot machines, to keep users engaged.Duolingo's approach contrasts with other apps like Finch, as users spend energy to engage with the product rather than earning energy.The energy system maintains monetization constraints by offering unlimited energy to premium subscribers.Critics suggest that the energy system aims to drive conversions while improving engagement and reducing punitive measures.The tension between user engagement techniques and optimal learning science poses a challenge for educational technology.The energy system is designed to serve both user experience and business goals, potentially increasing engagement and conversion rates.The shift in Duolingo's mechanic reveals the sophistication of behavioral design in shaping user behavior through psychological principles.