Funny you should mention global data structures. Last winter, when doing Advent of Code, it took me an embarrassingly long time to realize that I didn't really need to be writing super well-factored Clean Code™ with no globals or anything like that to solve these problems. And, when I stopped worrying about that stuff, my code ended up getting cleaner and easier to understand and debug.

New hypothesis: Some practices make all the sense in the world in huge enterprise projects, and no sense at all in small utility projects.