Good Dog

Grave Stele of the Dog Parthenope
Marble
Castro, Metelin Island
Istanbul Archeological Museum

Engraving:

"His owner has buried the dog Parthenope, that he played with, in gratitude for this happiness.  Mutual love is rewarding, like the one for this dog:  Having been a friend to my owner, I have deserved this grave:
Looking at this, find yourself a worthy friend who is both ready to love you while you are still alive and also will care for your body when you die."

De Amicitia

Misfortune and time reveal the worth of a friend.  Shakespeare counters.

Sophocles, Oedipus Tyrannus 611-15 (tr. Richard C. Jebb): 

Creon: I count it a like thing for a man to cast off a true friend as to cast away the life in his own bosom, which he most loves.  You will learn these things with sureness in time, for time alone shows a just man; but you could discern a knave even in one day.

φίλον γὰρ ἐσθλὸν ἐκβαλεῖν ἴσον λέγω
καὶ τὸν παρ᾽ αὑτῷ βίοτον, ὃν πλεῖστον, φιλεῖ.
ἀλλ᾽ ἐν χρόνῳ γνώσει τάδ᾽ ἀσφαλῶς, ἐπεὶ
χρόνος δίκαιον ἄνδρα δείκνυσιν μόνος:
κακὸν δὲ κἂν ἐν ἡμέρᾳ γνοίης μιᾷ.

Euripides, Hecuba 1226-7 (tr. James Morwood)

Hecuba: For while prosperity never lacks fair-
weather friends, in bad times it is the good men
who show true friendship.

ἐν τοῖς κακοῖς γὰρ ἁγαθοὶ σαφέστατοι
φίλοι: τὰ χρηστὰ δ᾽ αὔθ᾽ ἕκαστ᾽ ἔχει φίλους.

Shakespeare, Troilus and Cressida 3.2.145-53

Ulysses: Time hath, my lord, a wallet at his back,
Wherein he puts alms for oblivion,
A great-siz'd monster of ingratitudes:
Those scraps are good deeds past; which are devour'd
As fast as they are made, forgot as soon
As done: perseverance, dear my lord,
Keeps honour bright: to have done, is to hang
Quite out of fashion, like a rusty nail
In monumental mockery.