The practice of public speaking is crucial when preparing for the UPSC interview, as it not only builds confidence but also enhances articulation and clarity in thoughts. By regularly practicing speaking, candidates learn to effectively convey their ideas and respond to questions succinctly. This skill is important for presenting themselves persuasively during the interview. Additionally, engaging in public speaking helps candidates manage interview anxiety and adapt their communication style to different audiences, which can be particularly beneficial in high-pressure situations like the UPSC interview.