Final answer:
The 4-year-old boy's behavior is indicative of successfully navigating the 'initiative versus guilt' stage of Erik Erikson's psychosocial theory of development, where he develops a sense of purpose.
Step-by-step explanation:
The behavior of the 4-year-old boy, who is eagerly exploring new experiences and constantly posing why-type questions, suggests that he is successfully navigating a developmental task within Erik Erikson's psychosocial theory of development. According to Erikson, personality development occurs through the lifespan in eight stages, each with its own psychosocial task that needs to be mastered. For a 4-year-old, this corresponds to the stage typically focused on initiative versus guilt, where the successful resolution of this stage's conflicts leads to a sense of purpose and initiative.