Some concepts within Carl Jung's theory of personality can be useful for a layman in interpreting complex Enneagram theory. Some of Jung's concepts that correlate to Enneagram theory include psyche, self, ego, persona, shadow, complexes, libido, progression, regression, extroversion, introversion, individuation, and self-actualization. Once you have gained an understanding of these concepts, you will have another leg up on comprehending how the Enneagram of Personality works.