Well, maybe this meme is dying down, but I happened to re-read Emily's Trans 101, Upgoer Five Style
and while it's good, I also couldn't resist writing my own version. Strangely enough, I felt like the limited vocabulary here helped me be clear, whereas when I was writing about my job, I felt too constrained by it in places (possibly because of having to circumlocute for technical terms, which was less of an issue here.)
Most people think that when a baby is very little, they can tell whether the baby is a boy or a girl. Also, they think that every baby is either a boy or a girl, never both.
They think this because they think that what a baby's between-the-legs looks like tells you whether the baby is a boy or a girl. But that's not true. Both boys and girls can have one kind of between-the-legs. And both boys and girls can have the other kind of between-the-legs. It's how you feel that makes you a boy or a girl, and babies can't talk to let other people know how they feel.
Also, there are more ways to feel than just boy or girl, and you can also feel any or all of those ways no matter what you have between your legs.
Some people think that everyone has a mark inside their cells that says they're a boy or that they're a girl. This, too, is wrong. These marks are real, but it's people who decided that one mark makes you a boy and the other mark makes you a girl. People are wrong sometimes.
Most people who get called a boy when they're a baby are boys, and most people who get called a girl when they're a baby are girls. It's harder for girls who got called boys, and boys who got called girls, and people who aren't boys or girls. There are two different ways in which it's harder.
First, some people have a picture of their body inside their brain that's of a body that looks and feels different than how the rest of their body is. You can't change that picture even by thinking very hard or getting help from another person. If you are this way, you have to change your body instead to make it match the picture in your brain.
Second, whether a person needs to change their body and does, or they need to change it but they can't, or they don't need to change it, many people aren't very nice to boys who don't look like they think a boy should look, or to girls who don't look like they think a girl should look, or when they can't decide if another person is a girl or a boy.
I'm in both the first and the second group. People thought I was a girl when I was a baby, but I was a boy. I didn't know this could even be true until I was much older. As soon as I found out that just because people thought I was a girl didn't mean I was one, I knew I wasn't a girl. After a while, I realized that I was a boy, and not someone who wasn't a girl or a boy. I was able to change my body to make it more like the picture that's built into my brain, so I'm much happier having a body now. And most people who see me realize I'm a boy without me having to tell them, which also makes me happy, because it was hard to explain to people who thought I was a girl that I was actually a boy.
It's harder for people who got called a boy when they were a baby but aren't boys, because lots of people are very afraid of people who they think have said no to being a boy. They think that someone else not wanting to look like a boy means being a boy won't be as fun for them. To deal with their fears about themselves, those people hurt other people. This gets in the way of the people who got called boys and aren't, who are just trying to live their lives.
You can make it better by believing people when they say that they're a girl, or that they're a boy, or that they're something else and not a girl or a boy. You can also make it better by telling people they are wrong when they make fun of others who they think are being boys wrong or being girls wrong. Check it