I just know. I can't begin to truly explain what that's like, it just is.
I've always known, I've only understood what I've known for the past few years, but I've always known, and evidence as clear as and including outright saying "I'm a girl" litters my life back to about 5-7 years old.
I know because I don't feel comfortable functioning as a male, in any way, shape or form. Because something in the back of my mind has always said it's not supposed to be that way, my entire life.
How do I know I'm doing the right thing? How do I know what I am? I simply 'do'.
I don't really care about the labels, I know what I am with clarity, others can define it however they like, it's all vague semantics anyway. But I do know I can't live as a guy, and I'd sooner be dead than try again.
But don't get me wrong, I did a lot of thinking about my reasons and certainties in the beginning. I spent a good 8 or 9 months solid of my waking life going over it before making the decision. In the end I never reached any conclusion where I could point to something tangible as the defining factor of my existence. What I instead reached was the understanding that I'd kill myself if I didn't transition then and later regretted it, and if it was the wrong thing for me despite everything I felt, doing it was the only way I was ever going to come to realize that.
So I went forward, and I can now say with 100% certainty that my feelings were correct. I don't know why, but for some reason I just can't be a guy, a lot of people have asked me what 'feeling' like the opposite gender is like. I don't know what they think my motivations are, but I just have to live with the fact they'll never truly understand, and that that's not their fault. I certainly can't explain it. It's a part of the human perception that can't be properly conveyed in words.
Sure I could say that it's that "I don't feel like I have the right anatomy", but that would be massively understating it. I sort of see it as there being 3 major gendered aspects of the human experience, social, sexual (not orientation) and physical. And for me, all 3 I perceive as being female orientated.
I could say that some doctor said they believed I was... but I honestly don't care what anyone who ISN'T me thinks I am, because I know they can't know what I know, because they're not me. They will always be missing something huge in understanding my experience of living, that's just the way it is.
I feel like my entire life has been leading up to transition, all it needed was a spark to set off my realization that transition was actually possible. I didn't know it was until just before I turned 20, everything that's happened since then has lead to where I am now. I wanted to be a girl when I was 10, I have internet accounts registered as female from when I was 13, I always knew, it was just a matter of time till I transitioned. I'm just glad I never spent much of my life living as a 'male', I didn't have a lot of the classic male experiences, and I'm glad that I never will. I'm sure some people would ask how could I know I don't want to be male if I never experienced it properly? Again, the only answer I have is 'I just do'.
So yeah, that's my explanation. Everything about this whole situation, the answer for me is 3 words.
I just do.
I hate being transgendered, I doubt a time will come where I don't hate it, I doubt a time will come where I don't still feel the pain of what I missed out on. I don't think of what I am as a 'gift', to me it's a 'curse'. But in-spite of that, I don't envy those of us who don't have the benefit of being as sure and absolute in their feelings. My 'choice' was a relatively easy one. I had almost nothing to loose from giving up my 'male' life, because my inability to lead said life had lead to me having very little invested in it. And for that I'm grateful.