To me, it is this private moment of realisation that "I have it in me" to do this kind of distance, casually - that feels like an accomplishment. More so than, say, an official brevet finish. It is not that I don't value organised events and their objective measures of performance. It's more that when doing an event, I already know that I can do it; I would not attempt it otherwise with all the logistics involved. In that sense, it feels not unlike taking a test based on material I've already learned. It's the learning itself that's thrilling. That "A-ha!" moment. Doing well on the test? It's nice, and often necessary. But it's not the same as the learning itself.
Maybe this line of thinking just means that I am hopelessly non-competitive. Or maybe it is simply not a good analogy. In fact almost certainly not. But there's a grain of something in it, somewhere.
Covering new distance, covering new material. And along the way that feeling of having truly grasped, understood, internalised something new - something that had previously seemed unattainable.