“It is difficult for an enemy to deceive
But it is easy for a friend to fool a friend.”
᾿Εχθρὸν μὲν χαλεπὸν καὶ δυσμενεῖ ἐξαπατῆσαι,
Κύρνε· φίλον δὲ φίλωι ῥάιδιον ἐξαπατᾶν.
Fool me once?
Theognis of Megara, a man with words for all occasions.