It was the cumulative effects of a lot of things, being stuck in a bad marriage to a disfellowshipped person. Being treated like a second class citizen because of that. Health and family issues that made it more and more difficult to live the JW life, and being judged for that. Having a better than average job where I was respected and paid the same as a man doing the same work made it odd to be treated as a "lesser vessel" by the brothers.
Learning to think logically and starting to question things, like the generation change, because i had been around in 1975 and didn't get how "this generation" could be more than one generation. Seeing the question from the readers about the UN and thinking, huummm.
I finally reached a breaking point and it all just hit me one day that there was no evidence that the Watchtower had any special knowledge or was in any way being directed by God.