It's a long way from the cup to the lips! Greek apophthegm. Translated into French during the Renaissance. The Wiktionary, although not entirely satisfactory, gives an approximate version. Many websites, on the other hand, make fanciful comments, each as wrong as the next, it seems to me. Even sexually vulgar and inept.

     Its meaning is banal and hardly needs to be explained at length. In fact, the story behind the proverb is precise enough to require no explanation. Anceus, son of Poseidon (Neptune for the Romans), would be the unfortunate hero, and not Anceus son of Lycurgus as suggested in the Wiktionary, both Argonauts and both killed by a boar. The confusion is due to a misinterpretation of a passage in Pliny the Elder, where he refers to a painting by Aristophon (the painter, contemporary of Alcibiades) depicting Anceus, wounded by a boar, with Astypalea beside him (L. XXXV, ch. XL, 13). Astypalea, mistress of Poseidon, is the mother of Anceus of Samos (Mythologie pittoresque universelle, page 267). The latter married Samia, daughter of the river Meander.

     Anceus, son of Poseidon, was tyrannical towards his slaves, whom he made work hard in the vineyards of his Samos estate. One of them, exasperated by her behavior, told her one day that he would not drink the wine she produced. As the grapes ripened, the harvest completed and the bunches pressed, Anceus asked the same slave to fill a cup with the wine he had predicted he would not drink, ironically reminding him of this.

     As he did so, the servant prophesied once again that many things could happen before the cup reached his lips.

     Just as he was about to drink, Anceus was warned that a monstrous boar was ravaging his vineyard. Putting down his full cup, he rushed to chase away the beast, which killed him (Zenobius, Centuria V, 71).

     So the goal is not always within reach, however close we may be.