Tend your own gardens, together. Seneca, Epistles 5.48.1-3

A nice meditation on friendship, from Seneca.

Ad epistulam quam mihi ex itinere misisti, tam longam quam ipsum iter fuit, postea rescribam; seducere me debeo et quid suadeam circumspicere. Nam tu quoque, qui consulis, diu an consuleres cogitasti: quanto magis hoc mihi faciendum est, cum longiore mora opus sit ut solvas quaestionem quam ut proponas? utique cum aliud tibi expediat, aliud mihi. Iterum ego tamquam Epicureus loquor? mihi vero idem expedit quod tibi: aut non sum amicus, nisi quidquid agitur ad te pertinens meum est. Consortium rerum omnium inter nos facit amicitia; nec secundi quicquam singulis est nec adversi; in commune vivitur. Nec potest quisquam beate degere qui se tantum intuetur, qui omnia ad utilitates suas convertit: alteri vivas oportet, si vis tibi vivere. Haec societas diligenter et sancte observata, quae nos homines hominibus miscet et iudicat aliquod esse commune ius generis humani, plurimum ad illam quoque de qua loquebar interiorem societatem amicitiae colendam proficit; omnia enim cum amico communia habebit qui multa cum homine.

I will respond later to the letter you sent me from the road, an epistle as long as your journey! I must take some time alone and ponder what I have to say. You also took your time to think through the perspective you offer, considering whether it was worth sharing. I will require even more time than you, won't I, since concluding an investigation requires more work than proposing it? So let each of us tend his own garden. Am I talking like an Epicurean again? Of course we care about the same events: I am not really a friend, unless whatever happens to you happens and belongs to me, too. Friendship makes us share everything, creating a fellowship that embraces all we own and are. As friends, we do not face fortune alone, whether it be good or bad. Our life is shared. It is not really possible for anyone to live well if he regards only himself, converting all things into his own personal utilities. You must eventually live for another, if you want to live for yourself. When we keep society well, observing our public duties with diligence and piety, it mixes us together with our fellow humans—teaching us that there is a law common to all mankind, and providing excellent occasion to nourish the interior, private society of friendship, about which I am wont to speak. The man who has many things in common with a stranger will share all things with his friend.