Homeopathy recognizes that, although many people may suffer from the same condition or disease, each person experiences it in a different way. And so it is the person with the disease that needs to be treated, not the disease itself. This requires a very individualized treatment approach.
At the heart of homeopathy is the ancient Law of Similars, often referred to as "Like Cures Like". This law states that any substance which can cause symptoms in a healthy person can cure those same symptoms in a sick person.
Take the simple example of a healthy man who drinks several cups of coffee in the evening. He will likely develop a racing, overactive mind and be unable to fall sleep. But when a different man visits a homeopath bothered by chronic insomnia, kept awake by racing thoughts (which are NOT caused by an over-indulgence in coffee), he would likely be helped by Coffea cruda, homeopathically prepared coffee.
But not everyone suffering from insomnia will be helped by Coffea cruda. Say a second person visits a homeopath complaining of insomnia. But instead of being kept awake by racing thoughts, she is worried about her sick mother for whom she has been caring. She also suffers tremendously from dizziness and motion sickness. The homeopath also observes that she answers questions very, very slowly. This set of symptoms would indicate a different remedy. With successful treatment, not only should she start sleeping better, but her other problems should improve as well.
Just as homeopathy does not have one remedy only for insomnia, three different people could visit a homeopath, all with different complaints, yet they all might receive the same remedy. Again, this is because the person, not their condition, is what needs to be treated.