"Don’t waste the rest of your time here worrying about
other people—unless it affects the common good. It will
keep you from doing anything useful. You’ll be too
preoccupied with what so-and-so is doing, and why, and
what they’re saying, and what they’re thinking, and what
they’re up to, and all the other things that throw you off and
keep you from focusing on your own mind.

You need to avoid certain things in your train of thought:
everything random, everything irrelevant. And certainly
everything self-important or malicious. You need to get used
to winnowing your thoughts, so that if someone says, “What
are you thinking about?” you can respond at once (and
truthfully) that you are thinking this or thinking that. And it
would be obvious at once from your answer that your
thoughts were straightforward and considerate ones—the
thoughts of an unselfish person, one unconcerned with
pleasure and with sensual indulgence generally, with
squabbling, with slander and envy, or anything else you’d be
ashamed to be caught thinking."
-- Marcus Aurelius, Meditations, Book 3, Verse 4 (Gregory Hays)