A doctor cut death rates by 90 % – and was mocked for it.
In 1847 Ignaz Semmelweis noticed in Vienna that up to 18 % of mothers died of childbed fever on the doctors' ward, but only about 2 % on the midwives' ward. Doctors came straight from the autopsy room. He introduced handwashing with chlorinated lime – mortality dropped below 2 %. His peers rejected him.
Useful: Data can be right long before the mechanism is understood.
Source: en.wikipedia.org