I'm currently going through a career change getting a master's degree in Data Science. Before that I taught remedial math and statistics at the college level and before that I was a flight attendant.
When I was 4 or 5 I asked my friend how to pray and I started praying regularly to "god" and to my grandmother. I never thought she as there or anything but I felt the existence of my grandmother. However, I never felt the existence of god. That's when I came to the conclusion no god exists. I have never come across anything that has caused me to doubt that conclusion, but I've encountered many things that have bolstered it.