You're meant to use `unsafe` as a way of limiting the scope of reasoning about safety.
Once you construct a `&str` using `from_utf8_unchecked`, you can't safely pass it to any other function without looking at its code and reasoning about whether it's still safe.
Also see the actual documentation: https://doc.rust-lang.org/std/primitive.str.html#method.from...
> Safety: The bytes passed in must be valid UTF-8.