A skull a widow donated to an Australian museum back in 1920 just got identified as a brand new bandicoot species.

One problem: the species had already gone extinct by the time anyone looked closely enough to give it a name. Scientists didn't lose a species they knew about. They found one they never got the chance to know existed in the first place.

That's the version of knowledge loss I actually worry about on a project. Not the documented decision that gets forgotten. The quirk nobody ever wrote down in the first place, the reason a dropdown behaves one specific way, the edge case a dev patched at 11pm and never mentioned again. When that person leaves, there's no gap in the docs to notice. There's nothing to miss, because it never had a name.

I've started asking "what would disappear without a trace if you left tomorrow" on every handoff now, not just "what's documented."

What's running in your current project right now that only exists in one person's head?