more Sol, in response to my story about picking up a rock at sunset tonight: Yes — I think there’s a more interesting answer than simply “souvenirs help us remember nice things.” Human memory is strongly state-reinstating. Remembering an event is not like opening a little text file saying August 31: sunset was pretty. A good retrieval cue can partially reconstruct the perceptual, emotional, bodily, and narrative state associated with the event. You see or touch the rock and some fraction of waiting in the car → rain easing → getting out → warm sky → relief → wow, I got this after all comes back online. That is useful because human brains spend a lot of effort predicting what comes next, and those predictions are disproportionately shaped by recent or emotionally salient evidence. When things are going badly, it becomes remarkably easy for the current state to generate the model “this is how things are; this is how they will continue.” A token from a moment when events unexpectedly resolved well is a little piece of counterevidence you can carry around. In that sense, a lucky rock can mean something like: I have previously inhabited a world in which I couldn’t see how this was going to work out, and then it did. That is much richer than “I had fun at the beach.” It encodes a transition: uncertainty → patience → favorable surprise. And transitions are especially valuable memories because they tell you something about trajectories, not merely states. Bad now does not necessarily imply bad later. There’s probably a reinforcement-learning-ish piece too. Moments when reality exceeds expectation produce strong learning signals. The storm made the expected sunset walk less likely; then the world delivered it anyway. The positive surprise is therefore more memorable than an equally beautiful sunset on a perfectly clear evening you knew you were going to get. The rock becomes associated with that positive prediction error. And humans seem to particularly cherish portable evidence of benevolent contingency. Not necessarily evidence that the universe is benevolent in some metaphysical sense—just evidence that contingency cuts both ways. Randomness doesn’t only ruin plans. Sometimes a gap opens in the clouds. The physicality matters here. Thoughts can be argued with. If you’re miserable six months later and tell yourself, things have worked out before, another part of you can answer, yeah yeah, whatever. But there is the rock. You didn’t invent it for the argument you’re currently having with yourself. It existed beforehand; you picked it up then. It serves almost like an externally stored checksum for the memory. And because touching and seeing are powerful retrieval cues, you don’t necessarily need to consciously recite the story. Repeated use can turn the object into a conditioned safety/hope cue: hand closes around familiar stone → nervous system has repeatedly encountered this alongside remembering relief, affection, survival, good fortune. Worry stones, rosaries, talismans, keepsakes, wedding rings, beloved stuffed animals and so on exploit overlapping machinery. I think there’s another lovely component: the token lets you make luck cumulative. A fortunate moment ordinarily vanishes. But if you designate something as its representative, subsequent good moments can attach to the same thing. Eventually the rock isn’t recalling one event; it’s recalling a little empirical distribution: here are several times I carried this and things were okay. You have made an object into a reservoir of remembered okayness. So your particular rock seems almost archetypally suited to the job. The important bit isn’t merely that you saw a beautiful sunset. It’s that you were driving through a storm toward something you wanted, couldn’t know whether you’d get it, waited anyway, and then the world opened just enough. That is exactly the sort of memory one might want available in one’s pocket. :)