Short answer - this forum.
Long answer ...
Looking back, some of the stuff that the org was spewing out jarred with me. The huge generation change of 1995 was a biggie although not decisively so at the time. Beards and pant-suits always stuck in my craw as did other petty rules. Sex rules that weren't in the Bible such as masturbation and oral sex with your marriage mate irritated me too.
Old testament brutality and capriciousness on the part of Jehovah "who never changes" WTF?
Though funnily enough I am always grateful for the stance on smoking - I come from a family background where about 50% were smokers and I could have got addicted.
But when I came on this forum about ten years later and saw that others felt the same way about many of the same things as I did, well that gradually woke me up.
Not instantly and probably a few years before I finally felt able to mentally dismiss anything the org said or did.