Robert Thurman, a Tibetan practitioner and scholar, gives a good example of how our happiness is inextricably intertwined with everyone else's. He asked that we imagine being on a subway car full of people — for all the rest of time! Some people on the car are quite content sitting there, reading their newspapers or eating their lunch. Others are agitated, upset, or angry for one reason or another, creating a lot of tension in the car. Given that these are our companions for eternity, rather than just until the next stop, what is the wisest course of action? What will bring the greatest happiness? Obviously, if in some way we can alleviate the distress of our fellow passengers, everyone enjoys the greater peace and harmony that ensue. Our own happiness ultimately depends on the happiness of others. We just often forget that we're all on this journey together.
— Joseph Goldstein, One Dharma