What is the meaning of [There’s many a slip ‘twixt the cup and the lip]

Dr brewer recounts the story of Ancaeus, the helmsman of Jason’s ship _Argo_
in Greek mythology. ‘He was told by a slave that he would never live to taste
the wine of his vineyards. When a bottle made from his own grapes was set
before him, he sent for the slave to laugh at his prognostications; but the
slave made answer, “There’s many a slip ‘twixt the cup and the lip.” At this
instant a messenger came in, and told Ancaeus that the Calydonian boar was
laying his vineyard waste, whereupon he set down his cup, went out against the
boar, and was killed in the encounter.’

Hence nothing is certain until you possess it.

##### See also:

* Catch your bear before you sell its skin
* Don’t count your chickens before they are hatched
* Do not halloo till you are out of the wood
* Never spend your money before you have it