Common subjects chosen as optional papers by successful UPSC candidates often include History, Geography, Political Science, Sociology, and Public Administration. These subjects are favored because they align well with the General Studies syllabus and facilitate overlapping content knowledge, reducing study time. Popularity can also be attributed to their perceived scoring potential and relevance to civil services. Candidates often select subjects in which they possess a strong interest or academic background, increasing their motivation and performance. Ultimately, the choice of optional papers plays a critical role in shaping candidates' success in the UPSC examinations.