The negative marking system in the UPSC prelims serves to discourage guessing. For each incorrect answer, a candidate faces a deduction of one-third of the mark assigned to that question. Incorrect responses consequently lower the overall score, directly affecting a candidate's ability to qualify for the next stages of the exam. However, unanswered questions do not incur penalties. This system emphasizes the importance of accuracy and well-considered responses over random guessing, prompting candidates to focus on quality preparation and understanding of the syllabus to improve their chances of success.