A motto here of my endless reading – Clement of Alexandria, quoting Heraclitus in his Stromata (4.4.2, via Loeb’s Early Greek Philosophy v.3 pg.161):
Those who search for gold dig up much earth and find little.
χρυσὸν γὰρ οἱ διζήμενοι γῆν πολλὴν ὀρύσσουσι καὶ εὑρίσκουσιν ὀλίγον.
possibly to be connected – for verb choice – with a brief quote from Plutarch’s Adversus Colotem (20.1118C, and Loeb pg. 159)
I searched for myself.
and – though the Loeb editors put it in a different section (pg 189) – with this from Diogenes Laertius (9.7):
He who travels on every road would not find out the limits of the soul in the course of walking: so deep is its account
ψυχῆς πείρατα ἰὼν οὐκ ἂν ἐξεύροι ὁ πᾶσαν ἐπιπορευόμενος ὁδόν· οὕτω βαθὺν λόγον ἔχει.