This prospective study adopted Vygotsky's concept of perezhivanie to examine students' lived experiences in learning mathematics and how they were related to subject choice plans and actual decisions. Most research has considered students' mathematics subject choice as a decision predictable using important cognitive and social variables. Due attention has not been given to examining how students' lived experiences in learning mathematics relate and contribute to their subject choice plans and decisions over time. Perezhivanie is a psychological structure for understanding dynamic influences derived from personal and contextual sources. In this study, two case studies were crafted using multiple data sources including interviews, observations, surveys and fieldnotes collected over three years on two achieving students who had studied in the same class. Despite this shared context, their perezhivanija differed, revealing complex dynamic interplay between factors derived from personal and external realms. This study described the identified perezhivanija of these two students and explained how they were related to their subject choice plans and their eventual subject choice decisions. The findings revealed that perezhivanija, including both heightened experiences and meta-experiences, were vital personal sources informing subject choice plans and decisions.