For instance I'm the old world, if you wanted to change an interface, you might have to edit 5 or 6 files to add your new function in the implementations. This is pretty routine and you won't need to concentrate that much if you're used to it, so you can spend that low-effort time thinking about the bigger picture.
I figured out some patterns in the way it behaves and could put more guard-rails in place so they hopefully won't bite me in the future (spelled out decision trees with specific triggers, standing orders, etc.), but some I can't categorize right now.