Same with anything. You can read about how to meditate, cook, sew, whatever. But if you only read about something, your mental model is hollow and purely conceptual, having never had to interact with actual reality. Your brain has to work through the problems.
GP says that they have to come back tomorrow and edit the code to fix something. That's a verification step: if you can do that (even with some effort) you understand why the AI did what it did. This is not some completely new domain where what you wrote would apply very clearly, it's just a codebase that GP is supposed to be familiar with already!