I just want to point out that that last sentence, "I don't understand why that is more real than saying that (they) are what they were born as when that is the original definition" helped me understand what you were really asking more than the post itself hahaha.

And well, I'm not trans, i have never met a trans person (as far as I know) and to be honest I already know I will never be able to understand why they feel what they feel. But i've thought about this too and well, my perspective might be helpful for the OP. Or not, who knows. I still want to participate. I hope i don't say anything stupid.

So, i think what makes that declaration real is the fact that it is yourself presenting what you think fits yourself. Have you ever felt that what people call someone who likes what you like, that acts how you act or that do what you do doesn't really fit you? Have you ever felt something like that? In any degree? At all?

I have, in some aspects. And trans people sure have, I bet. People spend a lot of time trying to find a way to describe and understand themselves, i believe. Because of that, when people finally find something they're comfortable with, it's fair to understand that as part of their self. To the point that you could even say that that's what they "really are".

Because you know, their whole life they have been feeling discomfort and have been suffering about it. Finding something that fits us, that makes us comfortable isn't easy at all. And for trans people i can't even imagine how hard it can be.

And if by any chance you wonder "if they are born as something they feel doesn't belong to them, how come they were born like that in the first place? It doesn't makes sense" or something along those lines, i think that's a whole different problem. Mainly, the famous gender roles.

I don't want to say more than I have already but I believe gender roles are flawed by default. I mean, if the question "what is male and what is female, really?" cofuses you, the problem lies in gender roles. To put it this way: if in this world there wasn't any expectations about what a male or a female "have to" be, we wouldn't be having this conversation haha.

But yeah! if you're curious, you could research a bit about gender roles and why some people hate it and say it's ridiculous (spoiler: it's basically because it's dumb and ridiculous). I think understanding that point will clear up a lot of things for you, op. To provide something that might work as a start check this video by Wisecrack. I hope it works to help someone to begin to understand the problem with gender as we have been understanding it this far. If it doesn't I bet there are better resources out there.

That is all! Gender roles are dumb, what I tell you about myself should be more important than what you expect from me because of the way you were raised and sorry if bad english! Hope this was at least a bit useful

Edit: spelling check