schoenen van ongelooid leer
From LSJ
καὶ οἱ ἀμαθέστατοι τῶν ἰατρῶν τὸ αὐτὸ σοὶ ποιοῦσιν, ἐλεφαντίνους νάρθηκας καὶ σικύας ἀργυρᾶς ποιούμενοι καὶ σμίλας χρυσοκολλήτους: ὁπόταν δὲ καὶ χρήσασθαι τούτοις δέῃ, οἱ μὲν οὐδὲ ὅπως χρὴ μεταχειρίσασθαι αὐτὰ ἴσασιν → the most ignorant of doctors do the same as you, getting themselves ivory containers, silver cupping instruments, and gold-inlaid scalpels; but when it's time to use those things, they haven't the slightest notion of how to handle them
