It’s not easy finding a language to talk about nonbinary experience, but I think this gives me a shot. Most people are right or left handed. Right is considered normal, left is more acceptable than it used to be. You can make this a male/female metaphor or a straight/gay metaphor if you like! I think it works best as the latter because left handed people used to come under a lot of pressure to try and act right handed.
Looked at from the outside, most bodies have discernible right and left sides. A person with a single dominant hand will likely lead with the foot on the same side as the leading hand. They will experience one side of their body as dominant and one side as less useful to them. Right and left aren’t abstract concepts at this point, they are names for a lived and felt difference in how bits of a person’s body works.
I don’t experience the right and left-ness in my body in the same way. I can lead with either side, hands or feet. I find it more convenient to write with my right hand, but my left handed writing is adequate. I iron left handed, I paint passing the brush back and forth. I don’t deny that I have right and left hands any more than I deny that I have a female-appearing body, but my experience of them is not the same as the experience of a left or right handed person. However, I can easily demonstrate to someone else how some of that ambidextrousness works. I can demonstrate that I can catch left or right handed. It’s much harder to demonstrate anything about how I experience gender.
In practice it’s much the same. I see other people leading with their maleness, or their femaleness. I see them having a dominant side, but the other side is still there. Some of them really can’t use the offhand at all. Some people probably could use their offhands pretty well if they invested some time in it. Many people assume their offhand isn’t up to much simply because they haven’t given it the same developmental time.
I see qualities attributed to right and left hands (strong, dextrous, good, evil, weak, unreliable, etc) that have parallels with the way we attribute qualities to gender (strong, dominant, delicate, weak, unreliable…) I see that in a culture where male and right handed are both treated as normal, it can be a challenge being female or left handed, and things aren’t set up to work for you. Even in small, stupid ways. My spell checker accepts ‘right handed’ but not ‘left handed’ as good grammar.
A person who mostly only uses one hand for all the things can, with a bit of effort, imagine how that might be different. I’m pretty confident that a person who experiences their body in heavily gendered ways might, with a bit of effort, be equally able to imagine what it might be like not to be like that – not necessarily how a specific other person experiences their body, but just the possibility of different experience. Once you can imagine difference, exactly how it plays out is less of an issue. What makes things difficult is when people who have spent their whole lives being told that their way is the only way, can’t flex at all when other people experience something else.
We tell each other stories about what is normal. It doesn’t make those stories a fair measure of anything, and to deny a person’s experience based solely on a story about normality, isn’t very helpful.