I am a former fundamentalist evangelical protestant. I was used to carrying around quite a load of cognitive dissonance, being that I worked in a science field. I suspended my disbelief for about 15 years.
The events which finally made the difference was when cancer came to my family. My husband contracted brain and spinal cancer. Through the horrifying couple of years that ensued, I started to see through the assurances. I gradually started stripping away my credulity, my assurance, and my faith in god and the church I was basically born into. I was surprised to find that after I took away all the beliefs about god that weren't helpful or were doing more harm than good, I had no 'faith' left.
Everyone thought I was angry at god. But once I allowed myself to think that there might not be a god and contemplate the implications of that, it just all made to much sense. It was like putting glasses on after fumbling though life with things out of focus. The clarity was amazing. I devoured all kinds of secular books about faith and belief in gods. I read about the history of christianity from a modern secular view point.
In the end I lost both my husband and my faith in god. But I gained an understanding and felt relieved to not have to try to defend an indefensible faith. I didn't have to be angry with god. I'm an atheist.