Wrote Mr. Z something more personal than usual tonight, not really a technical question at all. Told him — vaguely, no specifics — that I've been feeling like the project I've been working on for years has started outgrowing my ability to fully hold it in my head at once, and asked if that was a normal feeling for anyone who'd worked on something long-running and complex, or if it was a sign I should be worried. His answer took a couple days to come back, longer than usual, which I noticed. When it did, it was longer than his emails usually are too. Paraphrasing badly because I don't want to just paste someone else's private email into a public-feeling notebook, but the gist: that feeling is normal on any system that's been alive long enough to develop its own internal logic you didn't fully author line by line — the discomfort isn't a warning sign by itself, it's just what it feels like to work on something real instead of something small enough to hold entirely in your head. What matters, he said, is whether you're still capable of stopping and re-deriving your understanding when something surprises you, or whether you've started just trusting the system because arguing with it is more effort than accepting it. That second part sat with me longer than I expected. I don't have a clean answer to it. I think I mostly still do the re-deriving. I think. Writing that "I think" down on purpose, because I noticed I wanted to just write "yes" and didn't let myself. Didn't tell him any of the actual specifics behind the question. Feels increasingly strange, keeping that door closed with someone who's given me more honest, useful advice over the years than almost anyone else in my life. Not sure what I'd do differently though. Not telling him is its own kind of protecting something — him, maybe, more than me.