I have a tendency, when something is both of those things, to think: "It has NEVER been like this before. My brain was once resilient and responsive and young!" But, of course, when I was 12, I thought pretty much exactly the same thing.
I feel I should be more accomplished and talking about this in mellifluous tones on public radio when I say: learning is an odd and nebulous process. (The fact that I was briefly convinced the word I wanted there was "effluvious" is one of the reasons I'm unlikely ever to turn up on public radio.) It will never stop being strange to me that I am often unaware of the moment when my brain stops viewing a piece of new information as a foreign invader—and decides it's prepared to remember it in the future without conspicuous effort.
It will also never stop being strange to me that the feeling of putting something new into my brain is an actual distinct feeling: I might as well have a giant cartoon head, which I open up and physically stuff information into.
But eventually, my brain rearranges itself, and I forget how difficult it was at first to remember something. Brains are wily and unbiddable sons of bitches.