Letters from a Stoic by Senecaby Parker on TwosIf a thing is in your interest it is also in my own interest. Otherwise, if any matter that affects you is no concern of mine, I am not a friend. Friendship creates a community of interest between us in everything. We have neither successes nor setbacks as individuals; our lives have a common end. No one can lead a happy life if he thinks only of himself and turns everything to his own purposes. You should live for the other person if you wish to live for yourself. The assiduous and scrupulous cultivation of this bond, which leads to our associating with our fellow-men and believes in the existence of a common law for all mankind, contributes more than anything else to the maintenance of that more intimate bond I was mentioning, friendship. A person who shares much with a fellow human being will share everything with a friend.