Abstract: Jung suggested that innate sensitiveness predisposes some individuals to be particularly affected by negative childhood experiences, so that later, when under pressure to adapt to some challenge, they retreat into infantile fantasies based on those experiences and become neurotic. Recent research by the author and others is reviewed to support Jung's theory of sensitiveness as a distinctly thorough conscious and unconscious reflection on experiences. Indeed, this probably innate tendency is found in about twenty percent of humans, and, in a sense, in most species, in that about this percentage will evidence a strategy of thoroughly processing information before taking action, while the majority depend on efficient, rapid motor activity. Given this thorough processing, sensitive individuals readily detect subtleties—including whatever is distressing or threatening. Hence, as Jung observed, given the same degree of stress in childhood as non-sensitive individuals, sensitive persons will develop more depression, anxiety, and shyness. Without undue stress, they evidence no more of these difficulties than the non-sensitive—or even less, being unusually aware of supportive as well as negative cues from caregivers. Given this interaction, one treatment task is to distinguish the effects of such childhood difficulties from what does not need treatment, which are the typical effects of the trait itself on an adult without a troubled developmental history.