I was raised in a Catholic family, and went to catechism several times, but never went any further because my mom, as a divorcee, was not welcome in church. This left me the opportunity to study religion independently, and my mom invited me to try out other faiths, so I often accompanied friends to their churches, to see what it was all about. And while I was still a believer, I couldn't find any sect that matched my beliefs, because things the different churches said about the nature of God did not correlate to the information I'd acquired by reading the Bible independently.
Then, eventually, someone gave me a book which contained some well-known (but not widely expressed) information that contradicted some of the foundational assumptions of Christianity, and that was pretty much the end of my faith. I was about 21 at the time. Later I met my future wife, who was involved with one of those churches that puts the fun in fundamentalism, and she kept getting in trouble with them because she kept on questioning things, someone would give her a book to shut her up, which she'd read, and find it contained nothing that addressed her question. So, she brought some of those questions to me, I had answers, even if they were of the, "We're not really sure, but this is our best guess" variety, and she finally felt satisfied. So, there went her beliefs.
Now, we're on the opposite end of this conversation, because we're raising our little girl in an atheist family, and we're dealing with the difficulty of teaching her tolerance for the beliefs of others. Since my wife and I were originally believers, we have a respect for that perspective that she doesn't have.
What's interesting is that she's guilty of the same process that drives religion, which is to accept ideas as an article of faith, without really understanding them. She doesn't understand why she doesn't believe in God... she's accepting it as an article of faith, because her parents said so.
Mind you, this is the same kid who refused to believe us at first when we told her of dinosaurs and planets, because we've done a great job of teaching her skepticism via the method of amusing ourselves by answering randomly selected questions with nonsense.
