The answer resides in how people are socialized to understand and enact gender. A large body of scholarly research in social and developmental psychology has demonstrated that gendered behavior is learned: From a young age, boys and girls are encouraged to display stereotypically gendered behaviors and discouraged from displaying non-normative ones. Just think about the tradition of giving pink items to baby girls and blue items to baby boys. The preference for these colors has no biological roots; in fact, pink was once considered the more “masculine” color. Yet over time little boys come to prefer blue and little girls come to prefer pink; they are subtly rewarded for liking their respective colors and may even be chastised for liking the other color. Moreover, children pick up on subtle signals from their parents and important others who enforce gender stereotypes. For example, when donning female garments during dress-up, girls might be told they look pretty, while boys might be told they look silly. Children seek to fulfill gender expectations in order to secure parental and, later, peer acceptance. As we grow up, it becomes difficult to distinguish between expressions of gender we actually prefer and those we have been socially rewarded for.
As a result of this socialization, gender norms provide perhaps the most basic organizing framework by which people define themselves and others. And because they are widely shared and deeply rooted, they are extremely difficult to change. Thus trans people face a unique quandary.
Unfortunately, such situations most often mean that trans individuals are stigmatized-that is, socially devalued-providing a basis for discrimination against them.