A physician and immunologist, Honjo was awarded the Nobel Prize in 2018. Immunotherapy based on his discoveries have revolutionized the paradigm of oncological treatment. In this interview, Professor Honjo recalls his childhood in Japan, his initial passion for astronomy, his years in the USA, and using his intuition in exploiting the properties of the immune system against cancer, an advance that paved the way for personalized medicine. What role does serendipity play in the discovery process? What are the boundaries that science should never cross?