I ceased to believe in god when I finally let go of the idea that somehow suffering can be part of god's long term plan. After quite a lot of other sh1t happening, my 30 year old husband of 10 years suffered permanent nerve damage to his lower spine due to cancer. While he appeared to everyone else to be reasonably healthy, he was in fact unable to urinate. He also lost sexual function and partially lost bowel function. He had to self catheterize for the rest of his life. Which turned out to only be another year due to proliferation of tumours in his brain.
I am no philosopher. I find that when people are talking about hypothetical occasions of suffering and god's will, they can always come up with hypothetical ways that God could be working in the situation. So therefore, apparently, we have no right to judge it as unacceptable for an omnipotent god. I could dismiss hypothetical suffering as not being in conflict with an omnipotent god. I did for over a decade. I could, however, not dismiss the private indignity and pain he suffered daily as being somehow beneficial to something. No possible benefit could come of my husband being unable to urinate. No one will be inspired by a situation like that, and even if they were, it is abhorrent to think that it would in any way justify the suffering and indignity he went through. It was a humiliation that brought him to depression. I lost my belief in prayer then, and my belief in god followed along accordingly.
The christians in my life had many things to say about the situation. At the time, the things were often hurtful, even as they were trying to be encouraging. Things like 'it's all part of god's plan and god is always in control. You just have to trust in him.' It rang hollow. More than hollow. Horrifying really. It was better for us to just admit that 'sh1t happens' to everyone, believer and unbeliever, worthy and unworthy. He and I faced what came with courage. And I was proud of the depths of courage he and I found in the horror that came. He died almost four years ago. And it was my strength that saw the situation through to it's conclusion. Not god's grace. I was there for our two children through all of it. We came through it. There was no 'Footprints' poem moment where I realized that when my strength failed, that a magic daddy carried me. I found depths to my humanity I didn't know I had. I found wisdom in many situations that saw us through. I was proud of myself for that. And I was proud of my late husband for his dignity in facing death. I became an atheist at peace with the choices I had made given a tragic situation.