Every one of us has a dark side that is filled with primitive instincts. This dark side of us has been called the "shadow". The most effective way to keep it from doing damage is first and formost to acknowledge that it exists. People who don't shine a light on it are more prone to its influence.
"Unfortunately there can be no doubt that man is, on the whole, less good than he imagines himself or wants to be. Everyone carries a shadow, and the less it is embodied in the individual’s conscious life, the blacker and denser it is." Carl Jung
"To confront a person with his shadow is to show him his own light. Once one has experienced a few times what it is like to stand judgingly between the opposites, one begins to understand what is meant by the self. Anyone who perceives his shadow and his light simultaneously sees himself from two sides and thus gets in the middle." Carl Jung