The importance of optional subjects in the UPSC Mains exam cannot be overstated. Optional subjects can significantly influence a candidate's overall score, as they account for one of the major portions of the exam. Candidates can choose a subject they are passionate about or have a strong background in, allowing them to demonstrate their expertise. A well-prepared optional subject can boost performance and improve rankings. Therefore, selecting the right optional subject, understanding its syllabus thoroughly, and preparing diligently for it can mean the difference between success and failure in the exam.