I never did doubt actually... That is the key reason why I am still amazed that I was ever able to escape that brain washing cult religion. I really hate Christianity now. But anyway... I just wanted to know more about... I guess why things were the way they were, but from a more religious perspective I suppose. All religious websites were biased of course. I already knew all the arguments on Christian websites. So I quickly moved to atheist websites. I was not worried because of how strong my beliefs were. I figured all the arguments would be crap anyway. Well... that is when all the wonderful thinking started. Little bits and pieces of my life started coming together to unveil the truth I know today.
I've always been one to question things. The questioning started with the sexism in the bible (among other things). The bible is a most horrid book. And then I noticed the way Xtians behave. They do what they please and behave badly and then go to church and get absolution from it.
Then they continue about their business. Then they believe those crazy fairy tales.
I am educated in science and don't believe that nonsense.
When I was about 10 a friend died during unnecessary surgery. Somebody -- my Sunday school teacher? -- wondered aloud whether he was in a state of grace at the moment of his death. If so, he was already in heaven. If not? Well, he would already be in hell for all eternity. I thought "What kind of god would do something that disgusting to a kid? For that matter, how would anybody deserve that kind of treatment?" This was about the end of World War II. Should that happen to Hitler? If anybody deserved it, he would. But I couldn't consign even him to such a fate. Therefore, hell is a fraud. My other choice would have been to see that, if hell was allowed to exist, then god was a fraud. I wasn't ready for that yet.
My Dad is a Pentecostal minister and we grew up in a few VERY Evangelical churches. Lots of speaking in tongues, laying on of hands, "dig deep to donate to God", if it's not of God it's of The Devil, End of Days stuff.
I was exposed to a lot of people having very intense emotional reactions from a lot of adults being "moved by the holy spirit" type stuff and I noticed that never once, did I feel what they felt. I never heard the voice of the lord. Never felt moved to tears or compelled by any unseen force to do anything. Even when everyone around me was clearly sharing an experience, I was just a kid in the middle of it.
Whenever I talked to my Dad about it he just said to pray on it and to try harder to listen to The Lord.
I prayed, I read, I studied, I questioned, I got in trouble for asking questions and not accepting "because God" as an answer.
By about 14 I had sorted out that whatever it was that let people experience God, I just didn't have it. It took another 15 years or so or reading, studying, questioning every religion I could get my hands on to eventually sort out that it's all man made.
I started to doubt while in a Catholic school religion class. When a nun told me that when someone hurts me I should turn the other cheek, I was telling myself I had only two cheeks.
Years later I edited that. For a woman I really like, I have four cheeks.
For me it was bit by bit: understanding that the Bible did, in fact, contradict itself and that these contradictions were real, not just "apparent." Realizing that some of the stories, Job in particular, could not be literally true and still be describing a good and just God. Moving on to recognize that the diversity of human language did not begin at the Tower of Babel. There was no worldwide flood. Genetics teaches us that it takes longer than Noah's ark to bring us back to a common ancestor (why do we not know the name of Noah's wife, considering that we are all descended from her? You would think her name would be more widely known). Man was on earth long before the Adam and Eve story would have taken place.
Once you recognize Adam and Eve as a myth, the whole notion of Christ's sacrifice becomes impossible to accept as a necessity. And then you realize just how non-credible the resurrection story really is. BAM! You're done.
That's how it was for me, anyway.
I think I simply was lucky - there was no aha! moment.
I was born a non-theist and managed through chance and temperament to reject indoctrination. As a child, and much to the embarrassment of my parents, I was asked on two different occasions not to return to Sunday school until I stopped asking inconvenient questions and laughing at the "lessons." It never took root.
They sort of gave up on me after round two.