Practicing unforgiving, brutal honesty in a relationship will do more harm than good.

If you consistently express all the problems and complaints you have for a person you'll just end up driving them away. There are things better left unsaid. Yes, you should be able to be honest with your best friends, significant others, and family, but you should do so with the judgement in mind that they are human and not always capable of hearing every single negative thing you have to say about them, even if you later take it back.