Recently, this thing people call “transgender” has been a subject of many debates. The media has been using this because from a twisted point of view it looks like it is defying the basic reality that men are men and women are women, as a perverse degenerate method. So now men can choose to become women and women can choose to become men.
David Reimer is just one example of how gender is biologically determined, and not something that can just change. There are millions of examples like this across the world in people with abnormal sexual development, in babies born with ambiguous genital, a gender assignment is chosen at birth, and this assignment many times involves surgery. Approximately 40% end up rejecting their assigned gender, whether or not they were informed about their birth defect. Genetically normal XY males who are born with a condition called 5-ARD have a deficiency in the dihydrotestosterone hormone but normal levels of testosterone. Dihydrotestosterone is essential in the development of the external reproductive system, while testosterone is essential in the development of the brain and secondary sex characteristics. People with this condition are born physically appearing like normal females, and raised as females if their condition is not discovered, but when they are a kid they grow up persistently saying "I am a boy". Their parents may or may not be supportive of this, but their condition is discovered when they confusingly, naturally start to develop as male during puberty. 90%-100% end up living as a male by a adult. Similarly, females with congenital adrenal hyperplasia will often have an increased androgen level while developing and be born appearing externally like a normal male.
A mutation in the Y chromosome can cause the body to be completely unable to respond to androgens (CAIS). Which means that even thought the chromosomes are XY, it is impossible to develop any male characteristics.
Attempts have been made to raise these females as males, but in all cases they have rejected this. This is because there is no possibility that the brain had been masculinized, just as there is no possibility to develop as male during puberty, or to be born with a male reproductive system.