The variation in marks achieved in optional subjects during UPSC Mains can be influenced by several factors, including a candidate's inherent aptitude, preparation strategy, and subject familiarity. Aspirants who choose subjects they are genuinely interested in or have prior knowledge about are likely to perform better. Additionally, effective study materials, guidance from mentors, and consistent practice through answer writing can impact scores significantly. The exam format and evaluation criteria for different subjects can also lead to discrepancies in marks. Understanding these variables can guide candidates in selecting and preparing for their optional subjects.