Recede in te ipse quantum potes

Do you ask me what you should regard as especially to be avoided? I say, crowds; for as yet you cannot trust yourself to them with safety. I shall admit my own weakness, at any rate; for I never bring back home the same character that I took abroad with me. Something of that which I have forced to be calm within me is disturbed; some of the foes that I have routed return again. Just as the sick man, who has been weak for a long time, is in such a condition that he cannot be taken out of the house without suffering a relapse, so we ourselves are affected when our souls are recovering from a lingering disease.

To consort with the crowd is harmful; there is no person who does not make some vice attractive to us, or stamp it upon us, or taint us unconsciously therewith. Certainly, the greater the mob with which we mingle, the greater the danger.

The diagnosis is unflattering. The mob does not change your views by argument; it changes them by atmosphere — the first stirrings Stoics call propatheia, the involuntary pre-passion that slips past before you have agreed to it. Seneca describes himself as a convalescent who must avoid drafts. The image is generous to himself and unsparing about the rest of us — we are all that vulnerable, whether we know it or not.

But nothing is so damaging to good character as the habit of lounging at the games; for then it is that vice steals subtly upon one through the avenue of pleasure. What do you think I mean? I mean that I come home more greedy, more ambitious, more voluptuous, and even more cruel and inhuman, — because I have been among human beings. […]

The cure is not isolation — Seneca was not a hermit. The cure is curation: who you spend time with, what you allow to wash over you. Modern translation: be careful what you scroll past for an hour at a time.