slip 'twixt cup and preclear, many a

a Variation of the expression there's many a slip 'twixt the cup and the lip: a plan, intention, etc., may easily go wrong before it is fully carried out; nothing is certain until it is actually obtained or fulfilled. From a Greek legend of Ancaeus, the son of Zeus, in which it is said that while planting a vineyard, he was told by a soothsayer that he would never drink of its wine. As soon as the grapes were ripe, he squeezed the juice into a cup and raising it to his lips, mocked the seer, who retorted with the phrase "there's many a slip between the cup and the lip." At that moment it was announced that a wild boar was ravaging the land. Ancaeus set down the cup, leaving the wine untasted, hurried out and was killed by the boar.