I think it's something biological. I was born two months too early, so it's entirely possible I was born during a phase of getting testosterone in the womb, and later on would have received more estrogen and converted my male brain into a female brain. Unfortunately, I decided I was tired of being stuck in there and decided to make my entrance a little more grand than most babies do. (nearly killed both of us in the process too)
I don't mind being trans most of the time. The times it sucks are the times where my feelings and needs are completely ignored by those who love me. I know they're coming to terms with it, but it doesn't make it hurt any less. I may be being punished for something in a past life, or I may be living out a past life as a male. Who knows?
I've also heard that being a FTM may be something that happens when a FAAB is born after a MAAB. I was born after a son, so it's entirely possible that also has something to do with it.
It's also possible it's inherited. I've got high functioning autism. They're coming out with studies that it's being linked to your father being on the spectrum (my dad is DEFINITELY on the spectrum, but undiagnosed, and he also almost reaches the savant level of autism with math) Autism has a LOT of comorbidity with other "disordered" and my alphabet soup of what I've been diagnosed with over the past two or three years is quite a lot.
I don't blame any one though, and I don't really have many regrets. I chose to pursue this. I saw a video where it summed it up pretty well for me. Either transition. Go crazy. Or die. I reached the point where those were my only options. I'm already crazy. I don't want to die. So transitioning is the path I'm taking, the good lord willing and the creek don't rise.
:p