Think for a moment about yarn.
Wikipedia will tell you that "Yarn is a long continuous length of interlocked fibres" which if you think about for a moment will lead you to the conclusion that if you knit with a ball of yarn, in some respects by the time you are at the end of that yarn there's really no part in that yarn that was there when you started. There's an illusion of continuity, because at any given moment in time you're knitting with a bunch of fibres and you don't really notice as one fibre ends and another begins, even after all the fibres with which you started have ended and you're knitting with fibres you hadn't even imagined when you started.
It's even better when you think about knitting any item (say, an amazing Bojack Horseman sweater). because even if you wanted to use just one color, chances are your skein of yarn is not nearly long enough and so you'll have to use another skein or two, and splice them in with your first one, probably using spit. Which means that not only is the yarn within each skein you're using not really the yarn you started with, the skein you're using at the end of the sweater isn't the one you started with, and the whole thing just sort of looks the same, and held together by friction and spit.
Friction and spit. The similarity to company culture is obvious, right? :)
I was having lunch recently with a coworker who after six years had left our company. We were talking about some of the ways our company had changed in these six years (a forever in tech company terms), and was likely to change in the future. In thinking about some of the influential people with whom we work, he asked "How will things be after Alice* leaves? Or Bob*?"
And that's when I thought of yarn, and the useful illusion of continuity.
Alice will one day leave; so will Bob. Each fiber in the yarn that is this culture ends at some point. And if the frequency of departures is low enough, in the end little of this will make a difference and the yarn will be unaffected by these departures. Over time it will change, not in discrete shifts, but (probably) more gradually, perhaps even unnoticed.
This is good news and bad. The good news is that a certain (high enough) size and (low enough) turnover rate, we can be less concerned about the impact of any given person leaving on the overall culture; the bad is that the changes above are harder to notice than the big, "as of today we've implemented stack ranking" sort of traumatic changes, and it's a little harder to notice if we're going in the right direction (irrespective of the fact that the Boiling Frog anecdote is factually incorrect, it's still a useful metaphor).
As someone who's interested in having this culture go in a certain direction -- and ideally continue to go in that certain direction after he departs, this yarn metaphor helps in one other way. If all of us are nothing but fibres in this yarn of which we are composed, we can see our role not simply as adding to the strength of the yarn, but also to its color; and if we "bleed" our values onto the fibres near us, then these fibres will continue to be hued by their interaction with us after we leave.
As legacies go, it's not a bad one.
* Fictional names