It "clicked" much later, in two stages, using languages that were "kind of like" OOP, even if not rigorously so: LabVIEW, HyperCard, Visual Basic. I think VB had a decent strategy for introducing OO to the rest of us. Out of the box, it was "object based," meaning that you could use classes that had been created by someone else. For a bit more money you could buy the version that let you do full OO, but I never did that. But by being a user of objects, it gave you an idea of what you'd want if you could create them for yourself.
Nowadays of course people range from being bullish to bearish on OO, and I've had the experience of doing it badly and making a mess of things, when a procedural or functional model would probably be better.
Kind of a lesser issue is that I finally grasped how to work with a modern OS after laying my hands on the first couple volumes of the Win32 programmer's manuals, which I think were vastly less forbidding than Inside Macintosh.
