How do the billions of connections between neurons in our brain change as we learn and remember? This is the story of the discovery and the discoverer of synaptic pruning, the process of synapse elimination central to making us who we are. Taking the reader from Professor Peter Huttenlocher's childhood in wartime and post-war Germany to his emigration to the US to reunite with his mother and the launch and progress of a career in medicine and research, we uncover the motivations and process of scientific discovery that led to an unexpected leap in our understanding of the human brain. Decades after the discovery, the importance of synaptic pruning to early learning, autism, schizophrenia, Alzheimer's disease and other conditions are now in the process of being uncovered.