Final answer:
Jean Piaget developed his concept of object permanence by observing young children's expectation that objects continue to exist even when hidden.
Step-by-step explanation:
Jean Piaget developed his concept of object permanence by observing young children's expectation that objects continue to exist even when hidden. According to Piaget, young infants do not demonstrate object permanence as they act as if a hidden object no longer exists. However, infants who have already developed object permanence would reach for a hidden toy, indicating that they know it still exists.