Opposing signs in astrology represent contrasting approaches toward a common goal. The pair of Cancer and Capricorn share a theme of (self) parenting. Just like their rulers Moon and Saturn, each of them approaches the matter from a completely different standpoint.
The concept of self-parenting is most often seen in “inner child” therapy literature. Put simply, it means we take over the role of parenting our inner child (the child-like part of our emotions) when we become adults – so Moon and Saturn not only represent our parents, but also how we parent ourselves as adults later on.