Piaget's work provides the fundamental basis for understanding and appreciating the way in which children develop as thinking individuals. Recognizing the stage of development a child has reached can provide important information regarding expected behaviors that child should exhibit.
For example, based on Piaget's work, it is unrealistic to expect that a child of three years old will be able to sympathize with a friend who has lost a favorite toy. Children of that age are at what Piaget called the preoperational stage and view the world and everything in it from a very self-centered perspective. The child may understand that the toy was important to the friend but will not be able to identify with the friend's sense of grieving and loss. When that same child reaches the concrete-operational stage (ages 7-11), s/he will be more likely to comprehend the reasons for and emotions behind the sense of loss. When the child reaches the formal operational stage (ages 11 and older), s/he could help to develop a strategy to implement an organized search plan to relocate the lost item.