Encouragement is powerful and is much needed. However, encouragement is biodegradable. It needs to be given from time to time. Negative comments are even more powerful. It can debilitate a person. Experts say that for every one negative comment given and received, it takes nine positive comments to just recover and to break even. So be an encourager. Be more concerned with building up rather than constantly tearing down.
True friends say good things behind your back and bad things to your face simply because they care. This is just one part of the equation. The other part says that the person who wants to improve would take the criticism positively.
The same principle applies to giving and receiving feedback in the work place. Do not bear grudges when given negative feedback. Take it as a challenge to improve. And do not be harsh and rude with giving feedback as well. Be constructive and be encouraging. This is effective leadership at work.