Compare it to another modern language such as rust. Go does not have a stdlib mechanism for converting error types into each other (akin to rust's Into), it doesn't have the idea of mapping values together (akin to rust's carrier operator which is basically like monad do syntax), it doesn't have a way to create a list of errors by default (akin to 'cause' in rust), it doesn't have a way to generate concrete error types for your functions (like the 'failures' or 'error-chain' libraries in rust, which can't be written in go due to a lack of macros and generics and sum types).

It doesn't have a way to match on all possible concrete error values (akin to 'match' in rust or other sum-type things) or to do thing slike '.and_then' or '.map_err' or so on.

Go's error handling is downright insulting in a language that wasn't built at the same time as c.