Definition
This idiom is used to emphasize that many things can go wrong or change before a plan or intention is fulfilled.
功亏一簣
They thought the deal was done, but I know there's many a slip twixt cup and lip.
他们以为交易已经完成，但我知道事情在完成前仍可能发生许多变故。
They thought they had victory in the bag, but there's many a slip twixt cup and lip, so the game isn't over yet.
他们以为胜利在望，但事情在完成前仍可能发生许多变故，所以比赛还没结束。
Even when everything seems to be going smoothly, don't forget there's many a slip twixt cup and lip.
即使一切看似顺利，也别忘了事情在完成前仍可能发生许多变故。