All the suffering in the world comes from seeking pleasure for oneself. All the happiness in the world comes from seeking pleasure for others.
ShantidevaWhatever happens, I will not let my cheerfulness be disturbed. Being unhappy won't get me anywhere and will dissipate all my goodness. Why be unhappy about something if you can change it? And if you can't, how will being unhappy help?
ShantidevaThe hostile multitudes are vast as spaceWhat chance is there that all should be subdued? Let but this angry mind be overthrownAnd every foe is then and there destroyed
Shantideva