This means that no one is better at finding a wrongdoer than another wrongdoer. So if you do something wrong, then you would know if someone else followed your mistake, or you would know someone with the same quality as yourself, did the same mistake if that makes any sense lmao. The example will help better your understanding.

A person with an outwardly dominant, masculine, or aggressive personality, but who also enthusiastically takes on the submissive or "bottom" role in the bedroom.