Opening the book…
Almost nothing you build outlasts you intact, but the conditions you leave behind do. Being indispensable feels like value and is actually a failure of handover — it means the thing collapses or limps the moment you step away. The measure of your work is how well it runs without you.
Write down what only you know. Leave the workshop tidy, the documentation current, the passwords findable. Name the person who should take the thing over and tell them before you leave, not on the way out. Fix the annoying small thing you have been working around for a year.
Don't over-engineer succession for something temporary or trivial. And if you are leaving somewhere that treated you badly, you owe your colleagues a clean handover — you do not owe the institution your loyalty.