Depends what the purpose of the feedback is.
Quite often, when people want feedback after a competition, what they want is not just where they went wrong, but what they need to do to win the next time out. That puts the person they are requesting feedback from in a quandry, because there is no guarantee such feedback can be given equitably to all candidates/applicants. Some may ask and some may not. Even if everyone asked, would the feedback be equivalently informative across everyone? And even if it was equivalently informative across everyone, how the dickens do you end up being able to pick the next time out if everybody knows how to get 100%?
So post-competition feedback is tricky, and demands skill, restraint, and the right balance of forthrightness and vagueness.
Many of the feedback discussions managers have with staff can involve “bad news”. There is a terrific little book I sometimes recommend to people called “How to Break Bad News” by the late BBC comedy-writer-turned-clinical-oncologist Dr. Rob Buckman. It is a guide for medical professionals and, as you can imagine, coming from an oncologist, deals with fairly serious matters. But there is much that is generalizable to the work context. A nice distillation of it appears here: http://www.cpso.on.ca/members/resources/practicepartner/doctalk/default.aspx?id=2746