I was brought up as a Lutheran, going to private Lutheran schools for 12 years (Grade 1-12). At one point I was interested in being a pastor; I used to love reading the bible and learning about god and all that. I took all sorts of religious classes I didn't have to, I enjoyed it a lot.
And in 12th grade I took a "Christian Apologetics" class; that is, a class where they tried to teach us youngsters to defend our beliefs against people who would challenge them. It talked about archaeological and historical evidence for a while, but the core of the class ended up being "The bible says it's true and we believe the bible 100% so that's why it's true."
Of course, I thought that was a terrible argument, and I went online to do my own research so I could "properly" defend my faith using more historical and "scientific" evidence and other tangible things besides "The bible says it is true so it must be true".
And that's when I came to the realization that I was kind of in a bubble surrounded by people who never questioned the bible, and I began reading stuff online refuting basically every single thing I was ever taught about why we believe the bible is true. Didn't take long after that for me to realize there was no real reason for me to believe it other than the fact that it was what I was taught to believe. So I stopped.
There's not much more to it than that though, at this point I'm pretty much atheist I guess, though I like to have my own particular world view (vaguely related to shamanism-type stuff, but it's sort of a fun idea rather than a belief I shape myself based on). But it's interesting to see this "bubble" of my friends/family who are still Christian and how they seem unable to see it from my view, and unconditionally believe/preach stuff like Creationism and the like, that directly contradicts scientific knowledge/etc.