Opening the book…
It's tempting to feel secure by being the only one who understands a critical thing, but that's a trap for you and a risk for the team, because indispensability means you can never take a real vacation, never move to more interesting work, and are a single point of failure for something the business depends on. The people who advance fastest here are the ones who make themselves replaceable, who document, teach, and share until the thing they own can survive without them, because that's what frees them to take on the next, bigger thing. Hoarding knowledge feels like job security and is actually a ceiling, since you can't be promoted out of a role only you can do. For the team, bus factor is a real risk we manage deliberately, because 'only Sam knows how the deploy works' is fine right up until Sam is sick during an outage. Making yourself replaceable is the generous, ambitious move, not the naive one.
Write down how the things you own actually work, especially the tribal knowledge that lives only in your head, and put it where others can find it. Pair with people and let them do the scary parts while you watch, rather than always being the one at the keyboard. Rotate responsibilities so more than one person has touched every critical system. When you go on vacation, actually go, and let the documentation and the team you've prepared handle things, treating any gap that surfaces as a bug to fix, not proof you're needed. Resist the quiet pull to be the hero who's always called; being called constantly is a failure of preparation, not a badge. Measure your success partly by how well things run when you're not there.
Making yourself replaceable in your current role doesn't mean making yourself redundant; the point is to free you for harder problems, not to erase your value. And some deep expertise takes real time to transfer, so this is a steady practice, not something you finish in a week.