In the late 19th century the German Doctor Samuel Hahnemann devised, or more accurately pulled out of his ass the pseudo medical practice of Homeopathy. Dr. Hahnemann decided by fiat that a substance that would cause the particular symptoms of a disease would if given in small amounts treat beneficially the same symptoms of an actual illness. The idea was that like cures like. Now so far it doesn't sound too outrageous even though it smacks just a little like sympathetic magic. But then the major woo started to be added.