A doctor drank bacteria to convince his colleagues.
Into the 1980s stomach ulcers were blamed mainly on stress. After attempts to infect piglets failed, Barry Marshall drank a broth of Helicobacter pylori in 1984. Three days later he felt sick; by day eight an endoscopy showed massive inflammation. In 2005 he shared the Nobel Prize with Robin Warren.
Useful: A good theory doesn't win because it's true, but when someone produces the evidence.
Source: en.wikipedia.org