People’s motivations to partake in religious rituals often relate to external socio-cultural forces such as tradition, ancestry, and peer-pressure, or deep personal convictions centered around devotion, gratitude, or spiritual experience, among others. Simultaneously, however, devotees may also have pragmatic motivations for practicing rituals, such as the need for protection, wellbeing, or socializing, or may see those rituals as a means of fulfilling their wishes. Importantly, the deity addressed in the ritual largely defines the scope and area of divine intervention and help. But all else being equal, why do people choose to engage in the specific rituals that they do, especially given that some are much costlier than others? Our fieldwork suggests that perceived ritual efficacy could be a key cognitive factor at play: people seek rituals that they consider appropriate (in terms of their structure and focus) and proportionate (in terms of their costs) to their needs and expectations. This almost contractual logic of ritual performance is best demonstrated by the concept of promise that is quintessential to the biggest religious festivals of three Hindu communities in Mauritius discussed in this talk.