A colleague left in December who was, by some margin, the best in the studio at getting useful output from a coding agent. Within a week the rest of the team had roughly closed the gap, because most of what made him effective was not in his head at all.
Where the skill actually was
He was careful about scoping requests, patient about restarting sessions that had drifted, and disciplined about reading output rather than skimming it. Those habits matter and they are genuinely a skill. But the thing that made his sessions consistently better than everyone else's was that he had, over months, built up a private set of notes about each codebase's quirks — which service lies about its response shape, which migration is still half-finished, which test is flaky and safe to ignore.
Notes are not a durable asset until they are shared
None of that was written anywhere the rest of us could see. It lived in his prompts, reconstructed slightly differently every session, and it left the building the day he did.
What we changed
- A living conventions file per project, covering error handling, naming, data access, and the specific gotchas that used to live in one person's head.
- A "known issues" section that gets updated the moment someone discovers a quirk, not retrospectively when someone remembers to.
- Session retrospectives, briefly, where anyone who had a surprisingly good or bad session with an agent writes one paragraph about why, and it goes into the file, not into a chat history nobody rereads.
The measurable effect
Onboarding a new engineer to an existing project now takes noticeably less time to reach useful output, both from the human and from the agent they work with, because both are reading the same document instead of one of them starting from nothing.
Skill that only exists in a person's head is a risk with a name. The fix is not to hire people who never leave — it is to write the thing down.
What is still genuinely a skill
Judging when an agent's output is subtly wrong rather than obviously wrong, and knowing when to stop delegating and write the thing by hand. Nobody has found a way to put those in a file yet. We keep trying.