Final answer:
Erik Erikson is the psychologist who agrees with the statement about developing social traits through solving problems at each stage of life, as it aligns with his psychosocial theory of development.
Step-by-step explanation:
The psychologist who would agree with the statement that individuals develop good social traits through successfully solving their problems during each stage of life and that failure to do so can lead to problems at the next stage is Erik Erikson.
Erikson's psychosocial theory of development proposes that personality development occurs throughout the lifespan and that at each of the eight stages of development, there is a task that must be resolved. Successful resolution leads to a sense of competence and a healthy personality, while failure leads to feelings of inadequacy and potential problems in subsequent stages.