Civilized people are taught by logic, barbarians, by necessity, communities by tradition; and the lesson inculcated even in wild beasts by nature itself. They learn that they have to defend their own bodies and persons lives from violence of any and every kind by all means within their power.
All I can do is to urge on you to regard friendship as the greatest thing in the world; for there is nothing which so fits in with our nature, or is so exactly what we want in prosperity or adversity.