Plato, Letters 340d

ταύτῃ καὶ κατὰ ταῦτα διανοηθεὶς ὁ τοιοῦτος ζῇ, πράττων μὲν ἐν αἷστισιν ἂν ᾖ πράξεσιν, παρὰ πάντα δὲ ἀεὶ φιλοσοφίας ἐχόμενος καὶ τροφῆς τῆς καθʼ ἡμέραν ἥτις ἂν αὐτὸν μάλιστα εὐμαθῆ τε καὶ μνήμονα καὶ λογίζεσθαι δυνατὸν ἐν αὑτῷ νήφοντα ἀπεργάζηται· τὴν δὲ ἐναντίαν ταύτῃ μισῶν διατελεῖ. οἱ δὲ ὄντως μὲν μὴ φιλόσοφοι, δόξαις δʼ ἐπικεχρωσμένοι, καθάπερ οἱ τὰ σώματα ὑπὸ τῶν ἡλίων ἐπικεκαυμένοι, ἰδόντες τε ὅσα μαθήματά ἐστιν καὶ ὁ πόνος

and in this mind, that such a student lives, occupied indeed in whatever occupations he may find himself, but always beyond all else cleaving fast to philosophy and to that mode of daily life which will best make him apt to learn and of retentive mind and able to reason within himself soberly; but the mode of life which is opposite to this he continually abhors. Those, on the other hand, who are in reality not philosophic, but superficially tinged by opinions,—like men whose bodies are sunburnt on the surface —when they see how many studies are required and how great labor,