In my opinion, without sadness we cant totally appreciate the happiness given to us. If there were no sadness and problems, there would be no realisation of the happiness. Everything would be the same and there would be no interess for people to live and to achieve some purposes, and the life would be grey and colorless. There would be losted the point of the whole our living and the point of the whole our life. Sadness makes us to appreciate all the things that we have and all the people around us.