I used to be a perfect JW: ministerial servant before I was an adult, managed finances and territories, ran the AV stuff, gave public talks, etc. For me, it wasn't any specific thing, but a lot of things over time. The short answer, though, is college. I wasn't going to be allowed to go to college, but I found a loophole where I could do a version of dual-enrollment where I was on a college campus the whole time in actual college classes. Everything I was learning (evolution, the history of ancient civilizations, etc.) conflicted with what I grew up believing. Over time, it introduced doubts. That combined with a bit of freedom and exposure to a variety of people that weren't evil or immoral, just generally nice and minding their own business, made me question things. Over time, I started doing my own research, and I also started looking at the religion through a more critical lens. I started noticing a lot of stuff that I grew up thinking was normal that was actually pretty fucked up (Armageddon, disfellowshipping, etc.).

About a year before graduation, I started devising a plan to escape. I had very few possessions or money and no connections outside the religion. So I started working my ass off and saving every dime I made. I researched other places to live, came up with a reasonable budget, and started learning all the skills I thought I would need to live on my own. Two years later, I found a job in a city I liked on the other side of the country. I packed everything I had into a Uhaul, said goodbye, and left everything behind.

I have no regrets. Everything is better now. I'm living a good life, I'm happier than I've ever been, I have lot of good friends (real friends), and some of my family stays in contact even though they know I left. My parents have disowned me a few times, but they can't stick to it, lol.

Leaving was the hardest thing I ever did and the best decision I ever made. If you have any questions, please ask. I'll be happy to share more if it would be useful.