The programming languages you use, and the variety of languages you learn, deeply influence how you think about software design.
Software would be much more reliable (in general) if Erlang had become one of the dominant languages for development.
Go sacrifices too much for superficial simplicity; but I would like to see a language that's nearly as easy to learn, but has a better type system and fewer footguns.
Unit testing is often overrated. It is not good for discovering or protecting against most bugs.
Build/test/deploy infrastructure is a genuinely hard problem that needs better tooling, particularly for testability.