Final answer:
The defiance seen in the 'terrible twos' during Erikson's autonomy vs shame and doubt stage arises as toddlers strive for independence and make their own choices.
Step-by-step explanation:
According to Erikson, the defiance that accompanies "the terrible twos", a stage known as autonomy vs shame and doubt, usually occurs because the toddler is attempting to establish independence. This stage is characterized by the toddler's determination to do things on their own, such as choosing their clothes or dressing themselves, which is a manifestation of their budding sense of autonomy. If these attempts at independence are consistently thwarted, toddlers may begin to doubt their abilities, potentially leading to feelings of shame and low self-esteem.