What Did You Say?

is an excellent book (subtitled The Art of Giving and Receiving Feedback) co-authored by Jerry Weinberg (isbn 0-924771-33-X). As usual I'm going to quote from a few pages. I know I've snippeted this book before, but I read it again and a really good book deserves a repeat snippet. For the past year or so I've deliberately been re-reading books I've already read rather than reading new ones.
Cybernetics tells us that feedback is a relationship between two systems. ... you're a system too.
A lot of our fear of telling them comes from inexperience, or rather experience at giving feedback poorly and then getting a poor result. But getting a poor result is is such a terrible experience only if we have a perfection rule.
Over time, the process of sorting creates an environment that will not provide feedback that leads to change.
In other words, it's not so much the feedback that counts, but the struggle to get it - not the feedback, but the feeding-back.
If you keep doing the same thing why do you expect them to change what they're doing?
Say what you saw and heard.
If mistakes are not acceptable, learning is not possible.
Learning is what feedback is all about.