Plato

θαρρεῖν, ὦ Θεαίτητε, χρὴ τὸν καὶ σμικρόν τι
δυνάμενον εἰς τὸ πρόσθεν ἀεὶ προϊέναι.

No one should be discouraged, Theaetetus, who can make constant progress, even though it be slow.

Plato, Sophist.