The fox knows many things, but the hedgehog knows one big thing.

[πόλλ’ οἶδ’ ἀλώπηξ, ἐχῖνος δ’ἓν μέγα]

Archilochus (c. 680-645 BC) Greek lyric poet and mercenary [Ἀρχίλοχος, Archilochos, Arkhilokhus]

Fragment 201
    (Source)

As quoted in Isaiah Berlin, The Hedgehog and the Fox (1953). The fragment is found in a group of proverbs collected by Zenobius. Alt. trans.:

• The fox knows many things; the hedgehog one great thing.
• The fox knows many tricks; the hedgehog one good one.
• The fox knows many tricks; and the hedgehog only one; but that is the best one of all.
• Fox knows many, Hedgehog one solid trick.
• Fox knows tricks and still gets caught; Hedgehog knows one but it always works. (Source)