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.