 Edward Jenner could discover the smallpox vaccine before the virus, antibody, and immune responses were discovered. Cuckoo, a bird that had intrigued philosophers and naturalists since the days of Aristotle. It is known for its brood parasitism that is laying one's eggs into the nest of another. It was widely believed that the mother cuckoo evicts the eggs of the host. Edward Jenner first discovered the parasitic nature of cuckoo hatchling that evicts the eggs and chicks of the foster parents from the nest. But he could not convince the scientific world for his simple discovery. Later, the photographs and video evidence confirmed it. From the two instances of the life of Edward Jenner, we should understand. In science, credit goes to the man who convinces the world, not the man to whom the idea first occurs.