"I wouldn’t be your friend if everything that pertains to you were not my concern as well. Friendship creates between us a shared interest that includes everything. Neither good times nor bad affect just one of us; we live in common. And no one can have a happy life if he looks only to himself, turning everything to his own advantage. If you want to live for yourself, you must live for another. This sense of companionship links all human beings to one another; it holds that there is a common law of humankind; and if carefully and reverently preserved, it contributes greatly also to the maintenance of that other companionship I was speaking of, the one within a friendship. For he who has much in common with a fellow human will have everything in common with his friend."

• Seneca, Letters 48.2-4