It was a combination of things.
There was the 1975 lie (not that 1975 was the end, but rather, the lie that "Oh we never said that! You people just jumped to conclusions."). I knew I had read 1975 in Society's publications. So did my mother. So did another sister. It sounded so much like the excuse of Adam. "Well the woman you gave me caused me to eat."
Ray Franz disfellowshipping/apostasy rumors.
Hidden pictures of demonic faces in the Watchtower illustrations, even though the Watchtower was a letter from God.
AIDS is Jehovah's punishment for homosexuality, drug abuse, and hemophiliac blood transfusions. I thought Armageddon was supposed to do that?
Barney Clark's artificial heart. Obviously Barney had not become some sort of soulless zombie. So the belief that the heart was the JW true center of a persons feelings was poppycock.
There were also problems with the evidence not supporting the JW account of Creation. The aforementioned carnivores, for example. Big cats and dinosaurs eat meat. They were created to eat meat. They were not created to be scavengers. Fleas were obviously created to suck blood. JWs had theories that cats were tame vegetarians in Eden and then changed to meat eaters after Adam sinned. Well, then, why not just believe in evolutionary change over a million years instead. It is much more credible than the JW twists. Petrified rocks. Where did they come from? They couldn't happen in just 35,000 years. Oil? How did that oil get there if plants and animals were less than 35,000 years old?
So as I got older, and wiser, less and less things fit. And I got tired of trying to make them fit. And I wasn't happy. Why wasn't I happy? I was virtually a slave all of my life. They forced me to conform. The more they forced me, the worse the unhappy feelings became. So I decided to leave and live my life my way.
And even then I still worried that it might be the truth. But even if they were right, Armageddon hadn't come so far, so better to live my life for the remainder of it free, than live forever as a slave in what they call paradise. It wasn't paradise to me anymore.
So I took the plunge and left. Soon after I started to see things much more clearly. Now I know why nothing fit before and I am glad I took that step.
Tammy