This article originally appeared on Quora. Answer by Anders Andersen.
In my case: research into my beliefs.
Being raised as a Christian, I personally dedicated my life to serve God at age 20, and was baptized to symbolize that decision.
At age 35, something triggered me to actually critically review the reasons I had for my specific set of beliefs.
What reasons do I have to believe any god exists at all?
What reasons do I have to believe the Biblical god Yahweh exists?
Could the same reasons be applied to support the existence of any other entity (e.g. aliens from a distant galaxy)?
What reasons do I have to believe the Bible has a divine source?
Could similar reasons be applied to other so called Holy Books that I do not accept as divine (e.g. Quran, Book of Mormon, etc.)?
What scientific evidence exists to support my beliefs (e.g. Adam and Eve created literally 6000 years ago, evolution does not happen, a global flood destroyed everything except whomever was in Noah’s ark)?
Do I have any personal experience that shows beyond doubt that God is my friend, that He answers my prayers one way or another?
After researching all those questions in-depth, I realized I have zero reasons to believe the god I worshiped really exists.
Quite the opposite, all evidence seems to indicate that the Biblical God does not exist.
I also researched very much in-depth the history, scandals, teachings and practices of my brand of Christianity to see if my religion could really be divinely appointed as the one true religion. Guess what, they’re not.
And since I only believed in 1 god, the disappearance of my belief in him left me with belief in 0 gods. I am now an atheist, a result of critically reviewing my own beliefs.
And as far as I can tell, a very similar path was traveled by a large number of previously religious people who are now atheists.