Most personally convincing reasons you don't believe.

[Lucifer]

well, it's rather simple: I have looked for decades to find evidence for the religion that I grew up in, and gave the benefit of the doubt, but I found out that there was no evidence. I knew that I needed evidence to support my faith (I don't get why so many people say that belief does not require proof), so seeing that every place that I hoped to find evidence offered none at all, and seeing that there were a lot of people who benefited from fooling other people, I knew this was just a giant lie and I had to leave. The last confirmation came when I asked all my christian friends, one by one, when I told them that I left religion, "do you have any evidence for your religion? any good arguments? if you have any, I am all ear". I was sincere in this question, and no one could answer me. They are all intelligent people (with MScs and PhDs) who are very enthusiastic about their faith, so one would expect them to have anything to say, but they offered zero answers. I asked this question to dozens of people, without response. That gave me a lot of confidence to continue on my way out.