For instance, when I was young I once visited my parents' home; they had a cassette tape with some unfamiliar songs on -- sold for some benevolent campaign, I believe -- and among them was one I found spectacularly beautiful. It was a simple heartwarming song, childish really, but the melody was hauntingly beautiful to me. It was called "skopusser samba" (shoeshine samba) and may well have been my first encounter with the concept of samba. In any case, I realized that I would most likely never encounter it again by chance, so I committed the melody to memory to the best of my ability. And there it still is, so that I can sing it to myself in the middle of the night.
As I predicted, the song has faded to obscurity. Google found two references to it, both in Norway's national library, simple catalog entries. That's it.
You who are young today do not face such situations. Every song you hear is surely committed to the collective memory of the noosphere. Even the most trivial details of your lives and your times are archived and indexed. Born into an age where knowledge covers the earth like water covers the bottom of the sea, you don't really need individual memories except to maintain your identity. (Your schools are not yet aware of this, I suspect, though this may already be changing.)