As your baby progresses from one milestone to the next, remember that he doesn't really leave any of them behind. In order to grow and develop to his full potential he must continually build on and strengthen all of the steps that have gone before.
Stanley I. Greenspan (20th century), U.S. psychiatrist, health economist, and Nancy Thorndike Greenspan (20th century), U.S. psychiatrist, health economist. First Feelings: Milestones in the Emotional Development of Your Baby and Child, ch. 3 (1985).