I personally can't pinpoint one thing that changed my mind...there are so many reasons.
But I can pin point the moment when I started to take all the reasons seriously instead of dismissing them because I knew god was real. And that was the day I admitted to myself that it was 'POSSIBLE' I could be wrong, and asked myself how I KNEW god was real? Personally, myself, not anyone else. And I didn't KNOW. I had just never questioned myself honestly like that.
Even at that point though, its not like I lost all belief, I was just more open to really listening to both sides of the story for and against belief in a god. It was like my mind had been unshackled. I found nothing more than a desire for there to be a god. No evidence, nothing but an old book and people like me who WANTED to believe god was real.
I then read up on evolution. NOT from the creationist point of view, but the REAL evolutionary theory. I asked people to help me understand that because I just wasn't getting it, my prevoncieved ideas of what it was got in the way of me seeing the reality of it. Once I understood the basics I started to really understand the books I was reading. It all made sense. There is so much evidence for evolution it CANNOT be denied. Unless you don't understand it properly.
I have also discovered a love of learning about the universe. Everything I read about the universe, planets, stars and the earth leaves me in awe. The vastness of space makes our tiny planet seem insignificant. There is NOTHING like the universe to put life back into perspective.
So, it really is a journey to non belief. I suppose some people might wake up one day and think to themselves 'I don't believe in god', but for me it was a process...and a personal search with a lot of honesty to MYSELF. Before I could even entertain the IDEA that god might not even exist. At times this process was very painful. I will not lie to you. I felt grief at the loss of my long held belief. But now, in hindsight, I see the grief was the loss of a dream. Not the loss of a god.
The fact that previoisly I could not think that way, showed nothing but my personal bias towards a belief in god. It did not show that god was real. It is impossible to ask someone to look at that idea objectively when they do not comprehend it. But people will swear that they are and they do. It's hard to explain.
And, my journey continues and is more exiciting than ever before in my life. I now have a love of learning. I have learnt that there is so much more that I don't know than I do know. I have a thirst for knowlegde. The knowlegde of reality. NOTHING outshines the reality of life and the universe we live in. There is wonder in this life.
