I was brought up as a boy. That's what happens to girls born with transsexualism. Society conspires to lock you into your assigned sex. Once those words "it's a boy" are pronounced, then a boy you shall be. Your parents and others around you will expect you to behave the way they think a boy should behave. You will be segregated, to a greater or lesser extent, from girls. You'll be herded with other boys in school. You might even end up in a school in which there are only boys.
Your body is part of the conspiracy as well. You have a penis and testicles. Anatomically, you resemble your father. You're expected to be at least somewhat like him and to aspire to be more like him.
Puberty is a nightmare, when sex hormones kick in with full force. You're literally flooded with testosterone. Imagine the horror for a girl who hears her voice deepen and watches her body become more and more masculine. By the time the flood abates, the body is altered forever. The pressure to be a boy turns into even more pressure to become a man.
The conspiracy of parents, society, and anatomy to convince you that since you have boy parts you must be a boy somewhat resembles a phenomenon called gaslighting. Gaslighting comes from the film Gaslight in which a man conspires to cause a woman to lose touch with reality. He tells her what reality is, and she comes to doubt her own perceptions. That's what happens to someone born transsexual. It's not just people who treat you like a boy, and later like a man. Your body mocks your sense that you are really a girl. Between the two forces of society and anatomy, it's difficult to retain your own sense of self.
Some girls are born with such a severe case of transsexualism or such a strong sense of self or both that the conspiracy fails. Nothing can overcome their sense of themselves as female, despite what people say, despite how people behave, and despite what their own bodies tell them. They know that people and their body are wrong. They demand early in life, or relatively early, that the situation be rectified.
Others, for any number of reasons, do not have such a strong sense of self. They buy in to what those around them and their own bodies constantly tell them. They doubt their own perceptions. They are quite susceptible to gaslighting. They might even reach the point of believing that their perceptions are wrong or mistaken. The tragedy is that this situation can last much of a lifetime, even through marriage and having children.
Whether early or later, the situation must be rectified. The birth defect must be fixed. There seem to be a rare few who live with their birth defect for their entire lives, using various coping methods. But most are compelled to repair the damage so they can have as much of the life they always should have had as possible.