Most relevant to the current discussion are Roberts and colleagues’ “cumulative continuity principle” and the “plasticity principle.” These principles hold that personality displays increasing stability throughout the lifespan (past age 30) and that personality is always amenable to change. According to this perspective, personality stability continues to increase throughout the lifespan because individuals continue to develop their identity and select into environmental niches. Plasticity of personality follows directly from this logic, in that trait development is thought to never be “complete” and is thus always open to environmental manipulation. Several important life transitions, such as the entry into the work environment or into a romantic relationship, may thus explain the dramatic change in increasing stability around age 30. Stability is thought to increase following adolescence, as the experiences that shape children in high school and college become more consistent. After major life events, such as obtaining mature romantic or occupational roles, the environment has reached a relatively stable point.
