Because remembering PD39 he is saying that we try to make people into one family (or friends? Depending on the Greek)
It doesn't appear PD39 is even that clear cut. Several translators have taken the "things" approach and talk more about circumstances:
“The man who has made the best arrangements for the confdence about external
threats is he who has made the manageable things akin to himself, and has at least
made the unmanageable things not alien to himself. But he avoided all contact with
things for which not even this could be managed and he drove out of his life everything
which it profted him to drive out.” Inwood & Gerson (1994)
“The person who has put together the best means for confdence about external
threats is one who has become familiar with what is possible and at least not unfamiliar
with what is not possible, but who has not mixed with things where even this could not
be managed and who has driven away anything that is not advantageous.” Saint-Andre
(2008)
“The person who is the most successful in controlling the disturbing elements that
come from the outside world has assimilated to himself what he could, and what he
could not assimilate he has at least not alienated. Where he could not do even this, he
has dissociated himself or eliminated all that it was expedient to treat in this way.”
Strodach (2012)
Thanks again to Nathan for his list!!