For me, it's a mix of a lot of things. First, I guess I wouldn't be able to live without changing my body. I never had any ambition in life and whenever I started doing something, I'd either lose interest on it or become really good in no time - mostly because I would be bored and study anything I needed/wanted really fast, and then give up. Being the newest of three 'brothers' (even though I considered myself a man at some point, I guess it was all just an act of survival, since my whole family is harsh), at first I considered commiting suicide, but without courage to do it, changing my body became a priority.
Second, I started to look about it in an interesting way (after reading countless of kind words on this forum - thanks everyone

) - I know we're not perfect and sure there are girls out there who have the perfect bodies, but I don't actually need that body. All I need is someone to accept me for the way I am. And that will eventually come, no matter what (I guess). No matter what anyone says to you, it will come. Even though I really care about beauty and everything that comes with it, I'm fine being 'average' (or even 'below average' when it comes to beauty). But I won't stop pursuing perfectness, nor that perfect body.
Third, and this is much more personal, people say that the transition is like a hurricane, destroying everything on it's path. But I never had anything, so... Nothing to lose, I guess? I'm still sad my family won't accept me, but it doesn't matter anymore. I should live my own life instead of living someone's else.
Hugs and hope you can find your answers