Another one of those questions that could get a real quick short answer.  I thought my site already addressed such a basic issue, but perhaps I need to be a little bit more succinct and provide a nice short simple answer people can latch on to.

I never made a decision to be a girl.  I've always been one.   What I'm doing now is making my outward appearance match what I feel inside.  

This has an additional effect of allowing me to freely express my gender identity.  I have noticed, that people take me more 'seriously' now because I look like a woman.  When I still looked male, others seemed to find it hard to believe.   It's kind of like 'seeing is believing'.

For an excellent explanation of why transsexuals go through the trouble of altering our bodies, see chapter 6 of "Whipping Girl" by Julia Serano.

If you don't feel I'm addressing your question correctly, please rephrase it and I'll take another whack at it.