Positive feedbacks can make people happy and fulfill their requirement of achievement. It's the nature of human being. The praise will encourage us and make us work harder. In primary schools, the teachers praise the students when they make even minor progresses. The students will be very happy and study harder for the next praise. Furthermore, positive feedbacks make us feel more confident and we will feel more relax. This is very important in working since a person will make stupid simple errors when working nervously.
But negative feedback also has its advantages. If a person can only accept positive opinions, the horizon of the person will be greatly limited. He will think he has done all correct things and there are no need to adjust. On the country, negative feedback can figure out the weakness of a person or a group, and tell them the direction for improvement. When I studied in my university, my supervisor always told me to learn from the different opinions from my teachers and classmates and I really learned many things from the negative feedbacks. Of course, it's not very comfortable to be criticized by other people. But it's worthy to know your fault through that.
Only the friends who can give you sincere opinions are real friends. No matter positive feedbacks or negative feedbacks, the most important is to be sincere. When you give sincere opinions, your friends will feel that and think you are