Kagan believes that because of overly sensitive and timid children grow up shy and timid adults; approximately 15-20 percent of children are born with "inhibited behavioral manifestations," as he calls it. In infancy, these children are scared of all unknown. This causes them to be selective with regard to new products, unwilling to approach unfamiliar animals or places, and shy of strangers. This often makes them sensitive in other ways, for example, tend to experience guilt and to engage in self-flagellation. These children begin to experience literally paralyzing their anxiety in social situations: in the classroom and on the playground, meet new people and whenever they find themselves in the center of public attention. As adults, they tend to keep a low profile and pathologically afraid of speeches or speak publicly.