Perhaps it was a little absolutist. Maybe it would be better written like this:

If you're not familiar with implementing schedulers and concurrent systems then beware that implementing fibers from scratch is likely to result in some subtle and hard to debug problems.

If you have to use C/C++ you may well get better results using a library. If you aren't tied to the language then Erlang/Elixir, Go and Rust all have excellent implementations that have more language support.