I look back and remember moments in my life -- seemingly random, brief periods of time -- which I somehow attach a high sentimental value to. In themselves they are irrelevant but they unlock my memory of a state of mind I was in during that moment. Those moments truly are arbitrary -- for example, one of the strongest moments is linked to my memory of reading a local newspaper, sitting at a chair at my grandfather's place. The moments are very distinctive and highly discrete.
I haven't been able to figure out why this specific moment and not, say, the one that happened just after it, helps me unlock my memory. I did make two observations -- that enough time must pass to make a moment (the most recent moment happened to me three years ago), and that the time early in my life comes with more moments than the time later in life. The former makes sense -- enough time needs to have passed for the memory not to be fresh and easily recallable. As for the latter, I think it has to do with the fact that I perceived the world very differently, say, 20 years ago than I did 5 years ago, so it's more likely for a moment that happened early in life to unlock a deeper set of memories which are so unrecognizable (since I had a very different personality then).
I wrote down the moments I could think of -- there is a couple dozen of those -- but I don't like to go back to that list. There is something precious about "stumbling upon" these moments, as a chain of reasoning takes me back in time to ultimately land on one of those moments. Once I start thinking about the past, these special moments act as attractors -- I'm more likely to converge my thinking on a moment than not.
It's somewhat disappointing that the moments come at a decreasing rate. I really enjoy reminiscing about my state of mind and enriching the set of recollections like this would allow me to keep these memories fresh. Just like with a favorite song of yours, you can recall them too much and lose their magic.