As someone who deals with 15 million lines of code (and many readers of this have bigger systems) i need to trust that do X does X without me having to know how. When I have to learn it slows me down from the part of the code I need to know well. If do J is needed, that needs to be someone else's problem who knows the rest of do X. Unless do X is my responsibility of course. But nobody has responsibility for more than a small fraction of the code.
This is a great point often forgotten in this kind of discussion.
Size matters, and depending of the system size we’re dealing with it will have a significant impact on what approach we take. Or how we handle documentation for instance.
