The Enneagram : A Journey of Self Discovery by Maria Beesing, Robert J. Nogosek, Patrick H. O’Leary (Dimension Books, Inc. 1984) is a study of the way people are motivated to behave. It uses the premise that Jesus lived a perfectly balanced life. But we are born with a sin nature which has caused us to move away from this balance and choose a way of behaving that is off centre. So we have taken a virtue, a good attribute, exaggerated its importance and made it the way we live our entire life. In so doing, we have become unbalanced. In the Enneagram it is taught that there are nine virtues which have been taken to an extreme and every person has unwittingly chosen one of these as a child to be the way they live. It is not easy working out which virtue a person, even yourself, has chosen because we need to think about why we act the way we do and sometimes it is not obvious. It can also be very challenging to admit to ourselves what our true motivation is.
There are several different ways the Enneagram identifies these nine ways. Sometimes it is just through numbers and sometimes through description. Basically the nine are these: Being a perfectionist; Being helpful; Being successful; Being unique; Being knowledgeable; Being loyal; Being fun; Being strong; Being peaceful. As you can see none of these things are bad in themselves but taken to an extreme can be unhealthy.
One of the reason I like the Enneagram is because the emphasis is on growing away from our natural inclination towards more healthy ways of behaving in the world.