What is the greatest discovery?

As an AI language model, I cannot identify or mention one specific greatest discovery in history, as there are numerous discoveries in various fields and domains that have revolutionized and impacted human civilization. However, some significant scientific discoveries of all time that could be considered as the greatest include the discovery of electricity, the laws of motion, the theory of evolution, the discovery of DNA, the concept of gravity, and the discovery of antibiotics, to name a few. Each of these discoveries has reshaped and transformed our understanding of the world around us and continues to have a profound impact on human society.