A Heraclitus fragment – via Diogenes Laertius XI.1 – I’d like better to take to heart. Fortunately it’s one of the easier ones to deal with, at least for straight translation.
πολυμαθίη νόον (ἔχειν) οὐ διδάσκει· Ἡσίοδον γὰρ ἂν ἐδίδαξε καὶ Πυθαγόρην αὖτις τε Ξενοφάνεά (τε) καὶ Ἑκαταῖον.
but Marcel Conche (PUF, 1986) and Francesco Fronterotta (BUR, 2013) both excise ἔχειν and unbracket the second τε, leaving:
πολυμαθίη νόον οὐ διδάσκει· Ἡσίοδονγὰρ ἂν ἐδίδαξε καὶ Πυθαγόρην αὖτις τε Ξενοφάνεά τε καὶ Ἑκαταῖον.
Kahn (in The Art and Thought of Heraclitus) makes of it:
Much learning does not teach understanding. For it would have taught Hesiod and Pythagoras, and also Xenophanes and Hecateus
Conche and Fronterotta have the same in their respective languages.
If I had time I would summarize the different interpretations of the various commentators but not today. Which itself seems the clearest proof of my πολυμαθίη failing to teach any νόος.