Letters 104.21

If you would be stripped of your faults leave far behind you the patterns of the faults. The miser, the swindler, the bully, the cheat, who will do you much harm merely by being near you, are within you.

Change therefore to better associations: live with the Catos, with Laelius, with Tubero. Or, if you enjoy living with Greeks also, spend your time with Socrates and with Zeno: the former will show you how to die if it be necessary; the latter how to die before it is necessary.

Seneca, Letters to Lucilius 104.21, translated by Richard Mott Gummere