Faith.
I’ve never been one to have a great deal of faith in the supernatural. I’ve always been raised to trust my own senses and my own logic, and most importantly, to keep my mind open and working. However, every theistic religion I’ve ever been exposed to has demanded that I shut my higher brain functions down and accept their message without question or thought; I should trust the Bible/Quran/Bhagavad-Gita because the Bible/Quran/Bhagavad-Gita says I should trust the Bible/Quran/Bhagavad-Gita.
For a while, I was able to fool myself into believing that I believe, and fool others. Somehow I kept open a loophole in my logic to allow the existence of a self-contradictory and nonsensical deity, and I was able to follow along in hollow, meaningless rituals to please others. Only recently have I been able to admit that that loophole has closed, and now I can say that I see things as they truly are.
I am an atheist.