And Plautus:
"Feliciter sapit qui alieno periculum sapit."
Compare Terence, Heaut. i. 2. 36.:
"Periculum et aliis facere, tibi quod ex usu siet."
And Diodorus Siculus, i. ab init.:
"Καλὸν γὰρ τὸ δύνασθαι τοῖς τῶν ἄλλων ἀγνοήμασι πρὸς διόρθωσιν χρῆσθαι παραδείγμασι."
And Tibullus, lib. iii. eleg. vi.:
"Felix, quicunque dolore
Alterius disces posse carere tuo."
These indications may perhaps put your correspondent in the way of a more satisfactory answer to his question.