Institutional knowledge that lives in one person's head is a real operational risk, especially with technology systems that were set up once and rarely revisited.
Start with an inventory, not a manual
A living document listing every system, who the vendor contact is, where credentials are stored, and who currently manages it covers most of what's actually needed day to day.
Document the "why," not just the "how"
Step-by-step instructions go stale as systems change. A brief explanation of why a system is configured a certain way ages much better, and helps whoever comes next make good decisions rather than just following steps blindly.
Centralize access to credentials
Passwords and license keys stored in one person's password manager or personal notes disappear when that person leaves. A shared, access-controlled password manager solves this directly.
Review annually, not once
Documentation created once and never revisited becomes inaccurate within a year. A short annual review — even 30 minutes — keeps it usable.
The goal isn't exhaustive documentation. It's enough that someone new could keep the lights on without having to call the last person who left.