If you say there is many a slip twixt cup and lip, you mean that plans often go wrong before they are completed so you cannot be sure of what will happen. The building is due for completion in September, but as they say, there's many a slip twixt cup and lip. Note: People sometimes just say there's many a slip, or change the second half of the expression. But there's many a slip twixt now and the eight or nine months it will take the company to design and reopen a new café. Note: `Twixt' is an old-fashioned word meaning `between'.