I think what goes wrong with dividing is people truly just splitting the code into multiple files. I think the code should be split conceptually thus not just

I think what goes wrong with dividing is people truly just splitting the code into multiple files. I think the code should be split conceptually thus not just copy/paste part of code from main file to submodules, but split the code around some functional bounderies or concepts so that each file is doing one thing and compose those concepts into more abstract concepts. So that when I try to debug something I can decide where I want to zoom in and thus be able to quickly identify the needed files.