There's many a slip 'twixt the cup and the lip is an English proverb.It implies that even when a good outcome or conclusion seems certain, things can still go wrong, similar in meaning to "don't count your chickens before they hatch". The modern proverb dates to the early 19th century, with English-language predecessors dating back to the 16th century, based on Latin and Greek templates reaching back to at least the 2nd century.