> 'does everything look okay at this point?' than from a narrow 'I think the problem is this'.

Even in a small real world codebase with just a few tens of thousands of lines and a couple hundred possible user interactions, you need the intuition for "I think the problem is this" or you're gonna be there for the rest of the year stepping through the code. Once you've scoped the problem to a potential few tens of functions, then you can spelunk through it to find the exact issue.