This study investigates the psychological mechanisms driving Irrational Consumption Behaviour (ICB) among young Indonesian consumers in the context of the highly popular blind box phenomenon. Drawing upon the Stimulus–Organism–Response (S–O–R) framework, the research examines the direct and indirect effects of Perceived Uncertainty (PU), Instant Gratification (IG), and Perceived Scarcity (PS) on ICB. Data were collected via a purposive sampling method from 160 young consumers (Gen Z) and analyzed using Partial Least Squares Structural Equation Modeling (PLS SEM). The findings confirm that both PU and IG significantly drive ICB. Specifically, PU significantly increases IG, which subsequently encourages ICB, suggesting that the affective thrill of uncertainty and the resulting urge for immediate unboxing fulfillment are potent drivers. Most significantly, Perceived Scarcity emerged as the strongest predictor of ICB, indicating that marketing narratives emphasizing limited availability are the most effective psychological trigger for irrational purchases in this market. However, the study found no statistical support for the mediating role of IG in the PU-ICB relationship, nor for the moderating role of PS in the IG-ICB relationship. These results imply that scarcity and instant gratification predominantly operate as strong, independent motivators rather than as interconnected psychological pathways. Managerially, the findings underscore the need for marketers to prioritize ethical strategies, balancing product desirability with consumer education to mitigate the risk of exploiting psychological vulnerabilities in this financially sensitive demographic