For me it started with basic things such as:
Not agreeing with them that a loving God would be willing to destroy millions just for not being a JW.
Not agreeing that the self appointed Governing body were Jesus's mouth piece
And just having seen and heard various things in my 30 or so years as a JW ...you know...... those things that make you go HMMMMMMM.
etc., etc.
Then reading COC clinched it for me.
Eyes