The best engineers work to make themselves replaceable
I've worked in places where keeping what you knew to yourself was normal, and in places where people shared what they knew openly.
A culture like the first one costs the company, and it costs the person keeping things to themselves too. If you keep what you know to yourself, the person next to you tends to do the same. You never learn what they could have taught you, so you grow slower than you would on a team that shares. It's a tax everyone in that culture pays, including the business.
There's a second cost too, a smaller one. Staying the only person who can do a job makes it harder to move on to the next one. Making yourself replaceable protects the team's overall level first. It also frees you to take a promotion, a different team, or the next hard problem instead of the one you already solved.
You could call it making yourself obsolete. What becomes obsolete is you in the role you hold today, not you as an engineer. People tend to hear the second one, which is why the idea makes them nervous.
Hoarding knowledge is a tax everyone in the culture pays
Almost everyone has worked with a colleague who kept some piece of knowledge to themselves, and has seen the team or the company pay a high price for it. One person understands a part of the system, every decision about it has to go through them, and everyone else works a little slower. But the person doing the withholding pays too. Their colleagues know things they aren't sharing either, and that engineer never gets to learn them.
Engineers have a name for the extreme case: the bus factor, how many people would need to disappear before a project stalls. Most teams never hit that extreme, but they live a milder version of it every week. A deploy waits on one specific reviewer. An incident runs an extra hour because the person who'd recognize the error message is out. Onboarding drags because the real documentation lives in someone's head instead of the wiki.
None of that shows up on anyone's scorecard. It shows up as a company that moves slower than the sum of its engineers should let it move. It also shows up as engineers on that team plateauing earlier than they would somewhere more open. It's a lot of small dependencies, and none of them looks big enough on its own to be worth fixing.
Sharing raises the floor for everyone, including you
Taylor Otwell, who created Laravel, is a good public example of the opposite of hoarding. He was the framework's main maintainer for years. If anyone had a reason to keep everything in his own head, it was him.
In 2017, Matt Stauffer wrote about a question people in the community kept raising: what happens to Laravel if something happens to Otwell. According to Stauffer, Otwell had already answered it on Reddit about a year earlier: Jeffrey Way of Laracasts would take over, and Way already had access to everything needed to keep the framework and its products running.
Asked in a 2022 interview with Cloudways who would take his place, Otwell said: "There are several people who could take my place. Jeffrey Way, Adam Wathan, Matt Stauffer, and others could all keep the framework and its associated services going."
An open-source project survives one person getting busy or bored only if the knowledge of how it works isn't locked inside that person.
The same is true inside a company. Teaching someone else how a system works forces you to make the tacit parts explicit, the parts you'd never write down for yourself because you already know them.
Once that knowledge exists in a form somebody else can use, a few things change. That person can cover for you. The team's overall level goes up, because two people know it instead of one. And explaining it out loud usually surfaces a gap in your own understanding that you hadn't noticed.
Replaceable doesn't mean checked out
None of this means dumping your work on someone else so you can check out. If you hear "share knowledge" as "let others do your job while you watch YouTube all day," you've got it backward. A good multiplier teaches so the team can handle more together. That's different from moving your work onto someone else's plate so you personally can do less.
The test is the team's total output, not yours alone. If you hand something off and the team gets more done, you've multiplied it. If the same work just moves from your plate to someone else's, you've offloaded it. People on the team notice which one it is.
What if sharing gets me laid off?
People hoard knowledge for a practical reason. If they write everything down and teach everyone, they worry they'll be the easiest name on the layoff list. Most people in this field have heard about someone who trained their own replacement and got let go anyway. In a company that lets people go once their knowledge is written down, hoarding is a rational response to a bad incentive.
That's a problem with the company, not with the person who's afraid. A company that punishes people for making themselves replaceable is rewarding the wrong thing, and it gets hurt by that sooner or later. The team ends up depending on whoever holds the knowledge, and when that person leaves, the knowledge goes with them.
But hoarding has a cost too, and it's bigger than the one people are afraid of. You keep the one thing you already know. Everyone else keeps hoarding around you, so you never learn what they know either. That adds up slowly, month by month, and it's easy not to notice.
Good leaders share on purpose, and that's why companies look for "multipliers"
Liz Wiseman wrote a whole book about this, Multipliers: How the Best Leaders Make Everyone Smarter. A multiplier extends the intelligence and capability of the people around them. A diminisher shuts down the thinking around them, often without meaning to, until the team is running on a fraction of what its people know.
For Wiseman, good intentions don't decide which one you are. Most diminishers believe they're helping. What separates the two is what happens to everyone else's output once that person joins the team.
You've probably worked with at least one multiplier: someone whose presence on a team quietly raised what everyone else was capable of. That's why companies often look for multipliers when they hire. A team is worth more than the sum of its people only when several of them are raising everyone else's level instead of protecting their own.
Whether that's you comes down to a choice you make every week. You can keep the useful thing in your head, or put it somewhere the team can use it without you in the room. Putting it there costs you a little standing today. It's also what lets you eventually leave the job you have now for a harder one, instead of staying the only person who can still do it.