but fails miserably for the other 1%. the existence and experiences of that 1% doesn't invalidate our understanding of gender, it just refines it and expands it to better explain 100% of people, not just 99%.
i think of it a bit like newton's concept of gravity. einstein's theory of relativity refined our understanding and made us realize that newton's formulas weren't quite right. they served well for many ordinary purposes, but they failed miserably to explain certain situations such as the movement of stars where the relativistic effects are very pronounced.
relativity didn't completely invalidate newton's formulas, and they're still widely used in practice. but most people are now aware that in some cases, you need to think in relativistic terms.
i think of gender as two long lists of behaviors and traits and preferences and so on. there are a ton of habits and behaviors that are deemed either "boy/man" or "girl/woman" behaviors. so if you look at those long lists and say i'm on the "boy/man" side of nearly every one, then you probably thing of yourself as a boy/man. similarly for girl/women for that side.
but as you see, since it's a long list, there are actually plenty of boys/men who have some traits or habits on interests from the girl/woman side, and vice versa. so there's actually a bit of gender fluidity in all of us. but 99% of us feel comfortable saying we identify with one list or the other, even if we have a few items from the other list.
but for that 1%, either it's close to 50-50 from each list, or it depends on the circumstances. and for some, the list they identify with most doesn't line up with their body. our society says males are "supposed" to identify with the boy/man list, but it doesn't always work out that way.
and there are some who just think splitting those traits and preferences arbitrarily on to two lists is just silly and they refuse to play that game. they think of themselves as genderless or at least that gender is very unimportant to their sense of identity.
we're closing in on 8 billion people on this planet. what makes anyone think that every single one of them would fit neatly into a crude division into exactly 2 categories? especially something as complicated as gender?