For example, overweight children are noted to use excessive self depreciating humor, trying to pre-empt teasing, but not getting the message. But self depreciation is a defense mechanism that can get out of hand, be you fat, uncreative, unpoetic, or whatever. Humorous self depreciation is great for that which we can't change, but damaging for everything else. A fat kid can lay off the donuts and get outside more often, but a cripple has a much different kind of problem. In one case the self-depreciation is only postponing a much needed lifestyle adjustment, while the other its a way of dealing with a problem that just can't be fixed with a diet and exercise.
Constructive criticism is one form of good feedback, the other is blunt opinion.
But while both are important, most of us will deeply resent the latter unless it's positive. If sugar coated feedback becomes a substitute for real work satisfaction then you become a feedback junkie who can't quit. By Grabthar's hammer, what a burn. Feedback needs to be nasty and sting when it has to. There is no point in going for the perhiphery, make a stab at the beating heart.