Four-year-old johnny is having lunch with his mother and sister. when his mother pours milk in the children's glasses, she finds there is not enough to fill both glasses, so she carefully pours half of the milk in the shorter, fatter glass in front of johnny and half into a thin, taller glass in front of johnny's sister. immediately, johnny complains that his sister got more milk than he did, and even when his mother tries to explain that they both got the same amount, johnny insists he is right. in this example, johnny is demonstrating a lack of development in the area of