Icons are conventions. They only become meaningful by familiarity. If I give a look at my dock right now, I can't honestly say that there are more than 2 or 3 icons which unmistakably suggest which app they represent.
Mail maybe, despite all the loathe that people seem to have for the glassy aspect, clearly represents an envelope which is still a common object in everybody's life, I guess.
That button with a smiling face, a Finder, you say? And what is a "Finder" anyway? It makes sense only for a long-term user of Mac, i.e. it has an acquired meaning.
I guess that the notes immediately suggest an app somehow related to music, even for users who have never studied music: it's another universally acquired association, because otherwise it would be just another strange symbol.
And then there's AppleTV which is actually a text icon. Others are comically outdated: the stylised floppy disk for saving.
I still confuse the most used app of all, Safari, with Maps, and neither of them clearly represent what their corresponding apps do.
But that's it, really. all other icons make sense only after you learn about it. Which brings me to the point I'm trying to make: there's nothing immediate, innate about their meaning, rather it's the result of familiarity layered year after year, decade after decade.
Of course it's fundamental for a platform to preserve some continuity when updating icons and UI, to reduce the user's disorientation. And users, especially aging users (sorry, but I had to say this...), inevitably become more and more resistant to any change which force them to retrain their muscle memory. With some good reasons ("This is only disrupting me, I want to get things done!") but also a lot of delusional thinking when they try to convince themselves that icons were "instantly recognisable". They have never been. On any platform.