Your codebase is full of code nobody understood
There is code running in production right now, at companies you use every day, that nobody can explain. Not the engineer who shipped it, not the team that owns the service, not even the CTO who signed off on the architecture three years ago. The code works — it passes tests, clears CI, deploys without incident — and no human on the payroll fully understands what it does, why it does it, or what would happen if it did something else.