H and C because they go together.
"I was mad at my god(s) because of a book."
This video helped me to let go of "belief in belief", and a lot of stuff I read (mostly online but in books also).
O-Other My inability to reconcile religion with scientific fact led me to be an atheist
---and then eventually that led to F :)
I don't remember what lead me to first question religion and theism, but I know that reading The God Delusion made me more comfortable calling myself atheist rather than trying to fence-sit with the label agnostic (which I now know was an inappropriate use of the term anyway).
O: Every Saturday morning, these two guys would swing by my house and hand me an Atheism tract...
But, really, O: It took A LOT of independent studying (science, religion, Bible, etc) for me to realize that God wasn't real and that Christianity wasn't true.