Most studies related to judgment and decision-making have focused on judgments and decisions made for oneself ('I'). However, many judgment and decision-making situations in marketing, consumer behavior, and management involve decisions made for others ('others'), and there is virtually no domestic literature examining how judgments and decisions made for others differ from those made for oneself. Research on self-other decision-making differences has produced mixed results: some studies show differences between self and other decisions while others show no differences. Moreover, even among studies finding differences, conflicting results have been reported—some indicating greater risk-seeking (or weakened loss aversion) when making decisions for others compared to oneself, and others indicating less risk-seeking (or strengthened loss aversion). Therefore, research identifying moderating variables between self-other decision-making is of considerable importance. Based on prospect theory and psychological distance theory, this study examined the role of interpersonal regulatory focus (promotion focus vs. prevention focus) in gain-loss contexts (gain vs. loss situations) as conditions moderating self-other (self vs. acquaintance) judgment and decision-making, using financial products (equity funds) as experimental stimuli. The findings of this study are summarized as follows. First, decision-makers evaluated target products more positively in gain situations compared to loss situations, but no difference emerged between evaluations of products subscribed to by oneself versus those subscribed to by others (acquaintances). Second, the interaction effect between regulatory focus and self-other (acquaintance) decision-making was found to be particularly pronounced in loss situations. Third, gain-loss situations and regulatory focus served as significant interaction variables moderating evaluations and decisions for oneself versus others (acquaintances), and this interaction effect was driven by promotion focus. Specifically, under promotion focus, individuals evaluated products they themselves had subscribed to more positively than products subscribed to by others (acquaintances) in gain situations, whereas in loss situations, the negative evaluation of products subscribed to by others (acquaintances) was attenuated compared to products subscribed to by oneself. Fourth, when the other was set as a stranger (someone seen for the first time), the interaction between gain-loss situations and regulatory focus and the main effect of regulatory focus emerged only marginally. Specifically, no difference between regulatory focus conditions emerged in gain situations, but in loss situations, prevention focus evaluated products subscribed to by others (strangers) more negatively than promotion focus did. Fifth, the effect of regulatory focus on others in gain-loss situations appears to differ depending on who the other person is. The implications for marketing and consumer decision-making as well as theoretical and practical contributions of these findings were discussed.