The interviewer will ask this question to see your enthusiasm and passion for your profession. They want to see what drives and motivates you while gaining a sense of your energy. When responding, focus on something that relates to your patients rather than the salary or adrenaline rush you get from your job. For example, your favorite part might be working with a team to participate in complex thoracic surgical procedures to provide the best care possible to your patients or applying new, life-saving technologies that extend a patient's life.