What does this mean, There is many a slip between the cup and the lip?

This means that even though something may seem certain or guaranteed, there is always a possibility for things to go wrong or not turn out as expected. It is a warning to not take things for granted and to be prepared for unexpected obstacles or challenges.

The proverb "There is many a slip between the cup and the lip" means that it is easy for something to go wrong at the very last moment, even when it seems like everything is going well. The cup and lip are a metaphor for success, while the slip represents the unexpected event or obstacle that can prevent you from achieving your goal.