What are the personality factors which characterize an underachiver? The author looks into this problem from the viewpoint of psychoanalytic ego psychology. He considers 7 case studies of underachievers troubled with neurotic conflicts. That which is called a healthy underachiever is beyond the limits of this study. The hypotheses from this study are: 1) Using the concept “ego defense”, we can answer the question “Why do neurotic conflicts bring about underachievement?” whereas before, the expression “Neurotic conflicts bring about underachievement,?” didn't solve any basic problems. 2) For someone with a certain type of defensive ego structure, it is a threat to be also endowed with a high will to learn, because he must meet new situations which create anxiety. 3) The way that the ego defense mechanism urges him to avoid the learning situation, is a distinctive mode which helped him deal with his formative experiences. 4) Therefore, from the viewpoint of the theory of ego development, the typical crises of the ego structure at each developmental stage may be recognized as important contributing causes in influencing the learning process; and the crises help determine whether the process is positive or negative, positive being a coping response and negative being a defensive response.