The metaphor of the black box refers to what is not conscious for an individual about their trajectory, and which influences their relationship to the world, especially work and coaching practice. In this case, the reader will play a maieutic role (of questioning) to understand the process of becoming a coach, to open the black box of coaching. For that, the student will “meet” Leo, former president of a national association and an experienced managerial coach with 14 years as a manager in positions of responsibility and 17 years of coaching practice. In this case, Leo tells the story of his career transition to coaching. Analyzing the stakes of his career path in resonance to his position of coaching is key to understanding and appraising the practice of a coach.