Personally, for me it’s the idea that just because you don’t experience something (dysphoria, or being a gender other than what society expects of you) that doesn’t mean those experiences aren’t valid.
I get sooo tired of the response “I just don’t understand! I love being my AGAB! Why can’t you just get over it?”
CIS here. The way I see it, bodies evolve in all kids of ways in the womb. Some grow blue eyes, others are brown, some are blonde, others are ginger, some are born with a sixth toe on each foot, some are even born with both sexes.
I can’t see why people can’t grow a female brain in a male body or vice versa. Or some have the “programming” of both. Some others might be missing that code altogether.
I don’t try to understand it, it just happens. It just is.