Optional subjects significantly influence the final score in the UPSC mains because they carry substantial marks in the overall evaluation. A well-chosen optional subject that aligns with a candidate's strengths can improve performance significantly. Since candidates have to write extensive papers on their chosen optional, proficiency in the subject can lead to better elaboration of answers, thorough analysis, and higher scores. Additionally, some subjects are seen as scoring more easily than others, making the choice of an optional subject a critical factor in achieving a favorable outcome in the examination.