Cognition (knowing) is a semiotic process. Learning by experience requires inquiry, involving abductive, deductive and inductive reasoning in a quest for what Heraclitus calls the logos.
Why is it so difficult to discover? In the first place,
ἐὰν μὴ ἔλπηται ἀνέλπιστον οὐκ ἐξευρήσει, ἀνεξερεύνητον ἐὸν καὶ ἄπορον.
He who does not expect will not find out the unexpected, for it is trackless and unexplored.Heraclitus, Kahn VII
χρὴ γὰρ εὖ μάλα πολλῶν ἵστορας φιλοσόφους ἄνδρας εἶναι.
Men who love wisdom must be good inquirers (historas) into many things indeed.Heraclitus, Kahn IX
But:
πολυμαθίη νόον οὐ διδάσκει.
Much learning (polymathia) does not teach understanding.Heraclitus, Kahn XVIII
ὅσων ὄψις ἀκοὴ μάθησις, ταῦτα ἐγὼ προτιμέω.
Whatever comes from sight, hearing, learning from experience: this I prefer.Heraclitus, Kahn XVI
But:
κακοὶ μάρτυρες ἀνθρώποισι ὀφθαλμοὶ καὶ ὦτα βαρβάρους ψυχὰς ἐχόντων.
Eyes and ears are poor witnesses for men if their souls do not understand the language [if they have ‘barbaric souls’].Heraclitus, Kahn XIV
What “language” do eyes and ears speak to the soul? That depends on how the soul is embodied, how events in the nervous system become significant, how perception works.