. Prov. Many things may happen to prevent you from carrying out what you intend to do. Bob: Now that I have a contract with a publisher, nothing in the world can stop me from writing this book. Alan: Don't be so sure. There's many a slip 'twixt the cup and the lip.
something that you say in order to warn someone not to be too confident about the result of a plan, because many things can go wrong before it is completed We still might finish in time for the deadline, but there's many a slip twixt cup and lip.