Meus mihi, suus cuique est carus.
(Plautus, Captivi 400)

(The one who is) mine is dear to me, (the one who is) another's is dear to
him/her.

(Pron = MAY-oos MEE-hee soos KWEE-kway ehst KAH-roos).

Comment: These few words of exchange caught between two characters in one of
Plautus' plays capture why it is that we human beings, finally, cannot be lone
individualists. We know how each other feels. It is also probably a strong
element in the success of Plautus' plays (or any good theater/drama)--it taps
common human experiences.

Who is dear to you in life? It is difficult to be human, draw breath and not
have a response to that question. If you can connect with the feelings and
experiences associated with having people in your life who are dear to you,
then you also know, approximately, what I experience with regard to my dear
ones, too. You know what being connected to others is like, so you know,
approximately, what my life is like, too. And I know yours, approximately.

Which is why war and violence are never just someone else's problem, and why
every religion and ethical system that human beings say we believe in all have,
without exception, some version of: do unto others as you would have them do
unto you.

It is because we know each other. We know each other's experience. We know how
the heart feels when it is broken. And one would have to be inhuman to ignore
that experience.