At 2am, the on-call alert fires. Checkout is degraded. Orders are not completing. The engineer who built the payment integration left six months ago. The runbook is three versions out of date. You have a distributed system you did not build, a failure that is active, and no time to read documentation.
This is not an unusual situation — it is the normal situation for any technical leader who has joined a company, inherited a team, or scaled beyond the systems they personally designed. The question is not whether you will face unfamiliar systems. The question is how fast you can become productive on them.
The gap between reading a system in 90 minutes and reading it in three days is not intelligence. It is method. Engineers who get productive quickly on unfamiliar codebases are not smarter — they have a traversal strategy. They start at the right abstraction level, ask the right questions in the right order, and know when to stop reading and start forming hypotheses.