Organon §136

Even those symptoms that are only rarely brought forth in the proving of a medicine can be cured by that medicine when the symptoms appear in a sick person. 

A medicine, during its proving in the healthy state, cannot bring forth all of its condition-alterations in one person, but only in many different, diverging body- and soul-constitutions. Nonetheless, the tendency thus lies in it (§117) to arouse all of these symptoms in each person according to an eternal, immutable natural law by virtue of which all of a medicine's actions, even those seldom brought forth in healthy people, are brought to bear in each person to whom it is administered who is in a disease state of similar ailments. Homeopathically chosen, the medicine then silently arouses, even in the least dosage, an artificial disease state in the patient that approximates the natural disease state. This artificial disease state rapidly and permanently (homeopathically) frees and cures the patient of his original malady.