Yes, "avoid global variables".

I forgot to write that one. In fact, I'd say, try to write everything as stateless as possible. That means no shared variables, functional style programming whenever possible (and logical, not for the sake of it).

Debugging a code base with global variables vs. passing what it needs is far easier to reason about when reading the code, but also easier to write tests for. Very good point.

State is evil, but of course you need some otherwise your software doesn't do anything real.