Doing good to other people is not mandatory. If you want to do good, do it warm-heartedly and towards all. Make no differences and help the ones that need help. Also, be grateful to those who helped you, to those who betrayed you, to those who disappointed you, to those who loved you, to those who lied to you, to those who bullied you, and to those who cared, as from each you learnt a lesson.
