Epictetus Enchiridion and Cebes Tabula (1660)

but you will certainly fail to attain those things by which
alone happiness and free-
dom are achieved.

Immediately then, practice saying to every
harsh impression phantasia: "You are an impression, and not at
all the thing you appear to be." Then
examine it by those rules
which you have; and first by this,
and especially: whether it concerns
the things within our power, or
the things not within our power. And if it concerns
anything outside of our power,
have this response ready: "It is nothing
to you."