‘Juicy’ or immediate abundant action feedback is widely held to make video games enjoyable and intrinsically motivating. Yet we do not know why it works: Which motives are mediating it? Which features afford it? In a pre-registered (n=1,699) online experiment, we tested three motives mapping prior practitioner discourse— effectance, competence, and curiosity—and connected design fea- tures. Using a dedicated action RPG and a 2x2+control design, we varied feedback amplification, success-dependence, and variabil- ity and recorded self-reported effectance, competence, curiosity, and enjoyment as well as free-choice playtime. Structural equa- tion models show curiosity as the strongest enjoyment and only playtime predictor and support theorised competence pathways. Success dependence enhanced all motives, while amplification un- expectedly reduced them, possibly because the tested condition unintentionally impeded players’ sense of agency. Our study ev- idences uncertain success affording curiosity as an underappre- ciated moment-to-moment engagement driver, directly supports competence-related theory, and suggests that prior juicy game feel guidance ties to legible action-outcome bindings and graded success as preconditions of positive ‘low-level’ user experience.