> My opinion is that if you can't reason about the code helping yourself with just a couple of additional messages the code is probably broken/too complicated to begin with and requires serious refactoring. I've never understood people stepping through a program hoping to find some mysterious creature somewhere along a huge stack of calls. In my career I have often seen people always debugging an application as a whole instead of separated modules. Dividing a problem is the key. The same key that allows me to still program using vim without autocompletion, keep APIs sane and coherent, and avoid dead code.

The big thing here is that you seem to only work with your own code, where you can arbitrary refactor it and keep the entire thing in your head, as well as quickly find which module does what. But when working with a large foreign project, none of this works. You have to start working at the scope of the entire program, because you have no idea of the internal structure yet. Of course, people who use debuggers divide the code up as they go, but the point here is that they place a few choice breakpoints at central points in the application logic, inspect the stacktraces when one gets hit, and use them to further dig in to the part of the code they need to look at.