…MBTI appears to be concerned with the conscious, cognitive part of the psyche, while the Enneagram is focused on unconscious, motivating forces in the depths of the psyche, perhaps associated with its archetypal structure. The two systems come at the psyche in two contrasting ways.
The MBTI starts with the assumption that there are four sets of fundamental choices, E/I, S/N, T/F, J/P, each of which are equally good. The description for each of the 16 types is presented in mostly a positive light. There is an emphasis on goodness--different styles and patterns, but the overall focus is on positive attributes. Only after one has learned the basic system, does one's attention go to the negative attributes of a personality, for example, when one is in the grip of the inferior function.
The early teachers of the Enneagram started with a consideration of negative behavior. In fact some related the different styles to the "Seven Deadly Sins" of the Christian tradition plus two additional "Sins" of Deceit and Fear. The learner may be asked to choose what is their chief fault, which lies at the basis of their life script. In Jungian terms, it is as though how we structure our Shadow archetype describes the underlying motives of our life. Enneatype descriptions can range from extremely healthy (noble or altruistic) to extremely unhealthy (psychotic).