David Amerland started doing karate at 13 years old, a new kid in a new school in Australia with nowhere to put his anger. He never stopped. Forty-seven years later he is a certified Taekwondo instructor who competed at black belt national level in Britain through the 1990s, a researcher who spent 10,000 hours studying neuroscience and interviewed 100 snipers to write The Sniper Mind, and co-founder of DareBee — a crowd-funded, entirely free fitness resource that serves around a million visitors a month globally and was used by Green Berets in Afghanistan.