Pinned has a second word inside it: pining. It has a bad reputation. It sounds like leaving your read receipts on: passive, a little pathetic, visible to everyone.
But keeping a thing and missing a thing turn out to be the same habit, aimed in different directions. You keep the ticket because part of you is still at the show. You keep the cassette because you still think side B was better.
We can make a pin for the ticket and the cassette. We cannot make one for the timing you missed, or the stop you should have gotten off at. So we press the small enamel version of the first thing, and let it sit near the second.