(Out)growing is a good notion indeed.
I met a number of JWs (especially at Bethel) who were way more critical of the organisation than I ever was -- and they are still in (or died in).
In my case months of reading (non-JW and non-religious literature), learning (Biblical languages), talking (freely) with a handful of close JW friends were involved. But were it only for that I could have remained a JW.
Looking back I think one very intimate moment (which apparently had little to do with all of this) was decisive:
As one very close friend of mine, with whom I had shared a somewhat unique experience of mutual understanding, was leaving Bethel, I suddenly realised how empty and meaningless my life would henceforth be. By "realised," I don't mean I was just afraid it might be so. I knew it would. Living on as I had previously been doing was simply unbearable. But as many in such state (whatever the reasons) I found a small secret door in the back of despair: shift from "living" to "watching". I had lost all interest in my particular part in the JW play (and the accompanying desires and fears) but I could still watch, with mild curiosity and a zest of desperate irony, what would happen next -- minute after minute. A very strange feeling of freedom and joy immediately followed this realisation.
Looking back, I think this very unremarkable "event" -- it happened as I was descending a flight of stairs in Bethel -- made me able to do what I had not been able to do so far. Breaking the circle on a tangential line. Allowing myself to act on what I believed -- and then to believe and think further -- and letting the rest fall behind, step by step. This attitude led me, with gradually increasing consciousness, out of Bethel and the WT within a few months. And through the rest of "life".