The sign Cancer represents the earliest beginnings of life; in the womb, in the tender care of the mother, and the early developmental influences of family life (including the father). There is a clear watery feeling to this sign; water represents our feelings. Those with Cancer, or its ruler, the Moon; strong in their charts usually prefer to live by the water. Water also pertains to the mind; the reflective, contemplative function of the buddhic consciousness.
The Crab, the symbol of Cancer, has its origins in the story of Heracles (or Hercules from Roman myth) and the multi-headed Hydra. The crab was the little beast that tried to pinch the toes of Heracles to distract him in his battle. Perhaps we can see that those things that distract us in our battles in life, are little indeed. Annoyances such as the crab can be swiftly dispatched with; as did Heracles, unceremoniously stomping it out of the picture.
The crab also symbolizes the sign Cancer with it hard outer shell protecting the tender parts within. Cancers, or those with strong Cancer emphasis in their charts, many times have a thick wall separating them from people in their environment. Presumably, they were hurt in the past, and their reclusivness inside their shell is a response.
Cancer, indeed being a water sign, can be quite sensitive; their inclination is to create a warm, nurturing environment. The tendency towards privacy in Cancers comes from the accentuation on the personal inner space which the home and hearth is so reflective of. Sentimentality, the preoccupation with the past, is another Cancerean negative tendency, since the thoughts and feelings can be a repository for memories.
Cancer’s connection to our early maternal influence and the feelings, calls to mind the the natural state of our emotions to be that of HARMONY with our environment. The concept of harmony then brings us to the other main task of our mother, to supply us with everything that we need, when we need it. A lack of harmony, therefore, brings an interruption in the flow of supply (money, food, etc.) into our lives; a coming back to harmony in our worlds; then, brings everything around again.
The Moon is the ruler of Cancer; and Jupiter is the exaltation ruler. Jupiter in Cancer is a very strong, protective influence. Jupiter is also the planet of abundance. Mars and Saturn are debilitated (hindered) in Cancer.