Who is gonna onboard those new engineers? I subscribe to Peter Naur's view of programming as theory building, the knowledge of what these applications running i

Who is gonna onboard those new engineers? I subscribe to Peter Naur's view of programming as theory building, the knowledge of what these applications running inside Twitter do is being lost on a fast pace, the code itself doesn't tell the whole theory behind the code. Institutional knowledge is necessary to sufficiently onboard any new hire, without that you have headless chickens running around trying to figure out what exactly are they working with. How do you solve Chesterton's Fence when there's no one around to tell you why the Fence is there?