I'm surprised nobody mentioned types or type systems as one of the best solutions for eliminating fear. Out of all the systems that worked on, the ones that were changed fearlessly were stuff written in Haskell and Purescript. That was before Rust became so popular. These systems were changed fearlessly and we had very minimal tests. The code reviews were much easier to perform as you don't tend to check if the code might throw exceptions but you just need to think about business logic.

These days I'd argue that Rust is at the same level of Haskell and Purescript in fearlessness.

Some languages that removes certain fears:

- Kotlin: removes the fear of null exceptions

- Go: removes the fear of forgetting about an error that this function throws

- Languages with ADT (Haskell, Rust ... etc): remove the fear of missing a case