Gender identity is described as an internal sense of yourself as male or female and needn't actually correspond to which sex you actually are. It's bollocks.
No, it isn't "bollocks" and as someone hospitalised multiple times over transsexualism I take exception.
Gender stereotypes as defined by society are utterly nonsense and cause a great deal of damage. There should be no rules attached to biological sex but there is. We are told that our biology must decide our hobbies, interests, career choices etc..
In rare cases the strict imposition of Gender roles and stereotypes creates a resentment of natal sex. Biology becomes seen as a barrier to block someone being themselves.
The situation is "I cant do x because boys don't do that, I'm a boy because I have male genitalia therefore I hate my male genitalia".
Granted this is rare but it still very much does exist.
As a child society told me that what I was didn't align with what a boy should be. My friends were girls and my interests were, according to society, only for girls. My internal sense from my youngest age was as someone who felt far more comfortable with female gender roles and stereotypes and male gender expectations caused significant distress. It is very much real.