I have been reading "Raising Children on Purpose" by Wesley H. Fleming (a very good book which I should be reviewing soon). In it, he writes "Research shows it takes ten compliments to balance the negative emotional impact of one criticism . . . You can't overdo it if affirmation is sincere." I think that is true. As someone who has been involved in creative ventures for most of her life (as an art major in college, as a graphic designer, and now as a writer), I have been subject to a considerable amount of criticism. While I like to think I have built up a thicker skin over the years, the truth is that it always hurts, and it stays with you a lot longer than the compliments.
There are different kinds of criticism - the constructive kind which offers concrete advice on how one might improve. This is a necessary kind - still painful, but at least useful. Then there is the personal criticism, when someone, just to be mean, tells you that they think you stink and have no value. This kind has no redeeming value and hurts horribly.
Sometimes, in parenting, we do need to offer constructive criticism, but it should be balanced with liberal amounts with praise for things done well. The second kind has no place in parenting, and I would venture to say, in personal relationships in general. It is painful and cruel and certainly against Jesus' commandment to love our neighbor. Next time you are getting ready to criticize someone (child, spouse, co-worker, total stranger) - think about why you are criticizing and the purpose of it. Choose your words carefully and act out of love, not out of anger or spite. Our words have tremendous power to both tear people down and build them up.