I am an atheist because I see no effects of God, god or gods in my interactions with the world.
This of course requires some explanation.
Theist: Have you looked?
Theist: I mean, really looked?
Theist: I don’t believe you!
S.A: I do experiments for a living.
My job is to work out what is going on in the physics of magnetic recording for hard disk drives. I take experimental magnetic disks and heads, put them together and attempt to understand the sources of observable changes. If God/god/gods wanted to communicate with me through fucking up my experiment in a recognizable way, they have had ample opportunity to do so. However, all fuck-ups in my experiment have had a recognizable source – me.
Conversely, all bright lights of understanding have occurred through discussion and argumentation of observations and hypotheses with colleagues and always have a physical basis. No God/god/gods are tapping me on the shoulder saying “Excuse me, I did that!”
Before doing recording physics, I was an astronomer. Again, I did experiments to try to understand the sources of observable changes and again, all the fuck-ups in my experiments had a single source – me.
Before I routinely did experiments for a living, I was a theist. For the last 17 years God/god/gods have had daily opportunities to point out their existence to me. That there has been no demonstration of that existence, I live and work as though they don’t exist. This is why I am an atheist.