The developmental precursors of the “fully functioning person” (Rogers) have not received much systematic attention neither in psychological research nor in theories of personality and its development. Likewise, the developmental conditions for maladaptive personality functioning and the formation of psychological symptoms have not been the primary target of research in clinical psychology during the past decades (Castonguay, 2011). On the basis of a theory of personality that specifies a functional architecture of personality (i.e., personality systems interactions theory: PSI theory) developmental pathways are described that promote successful or impaired development of the integrated self which plays a pivotal role in PSI theory. Adaptive developmental pathways are described in terms of the developmental conditions promoting the ability to initiate unattractive instrumental activities (action control) and the integration of self-alien and painful experiences into an ever growing personal knowledge base (self-development). Maladaptive pathways are proposed to describe the developmental conditions for two major forms of psychological disorders: symptoms related to impaired action control (e.g., procrastination, eating disorders, depression) and symptoms related to impaired self-growth (e.g., rigidity, failure to learn from mistakes, psychosomatic symptoms). Any theory of personality should be able to explain adaptive and maladaptive forms of personality development. However, this issue does not belong to the prime targets of research efforts made in personality, developmental, or clinical psychology. Instead, competing hypotheses are derived from global constructs such as self-effi cacy, irrational thinking, poor self-esteem and the like. Typical questions arising from this globalconstruct approach are: Does a man who has problems initiating simple activities at home (despite his effi cient performance at his work) suffer from impaired self-efficacy, poor selfesteem, or does he simply have chauvinistic attitudes against his wife? Global constructs are also offered by the two major schools of thinking in psychology: From a psychoanalytic point of view, a woman’s overeating may be caused by an “oral regression” which dictates her behavior to eat as impulsively as oral needs drive baby’s feelings during the oral stage of development? In contrast, behavioristic learning theory would attribute those and other symptoms such as disturbed sleep, impaired immune function and stress-dependent pain like headache or backpain to the acquisition of irrational thinking or maladaptive behaviors that can be remedied by rewarding more appropriate behaviors.