I used my brain.
Any specific info on what caused your leap from faith ?
Was it the fantasy, the reality, or the message ?
It's been eight or nine years now, so I don't remember all the specifics of my thought process at the time. I took a business law class in which the professor made us think critically. In order to get us to think critically about law, he spent the first couple weeks challenging our beliefs so that we could be objective.
Basically, I allowed myself to think about the stuff that I already knew didn't make sense. For example, in 9th grade, I asked my Bible teacher where Cain's wife came from since there were literally only three people on earth at that point according to Genesis, and, if there had been another woman, she would have been his sister. He said something to the effect of, "We don't know. You just have to have faith." Once I allowed myself to think about it objectively, I realized that inconsistencies like this mean it's either not true or omitting details, i.e. not the 100% literal, true word of God. "Have faith" just means, "Don't think about it."
Every explanation for every question involved some sort of convoluted mental gymnastics (like explaining the age of the earth and why God didn't just destroy Satan immediately to prevent all evil) when there are simpler and more plausible secular explanations with evidence.