there's many a slip

there's many a slip twixt cup and lip

proverb Even something that one feels confident will succeed can have disastrous problems before it concludes. "Twixt" is a shortening of "betwixt," an archaic form of "between." Everything seems to be going smoothly, but there's many a slip twixt cup and lip, so don't lose focus until we're over the finish line.
See also: and, cup, lip, many, slip, twixt
Farlex Dictionary of Idioms.

there's many a slip ('twixt cup and lip)

many things can go wrong between the start of something and its completion; nothing is certain until it has happened. proverb
See also: many, slip
Farlex Partner Idioms Dictionary

there’s ˌmany a ˈslip (’twixt ˌcup and ˈlip)

(saying) (of plans, hopes, etc.) nothing is completely certain until it happens because things can easily go wrong: We should get to London before 7 o’clock, but there’s many a slip ’twixt cup and lip. She aims to get to the top in the company, but there’s many a slip...
The word ’twixt is a short form of the old word betwixt, meaning ‘between’.
See also: many, slip
Farlex Partner Idioms Dictionary
See also:
  • there is many a slip twixt cup and lip
  • there's many a slip twixt cup and lip
  • There's many a slip 'twixt the cup and the lip
  • twixt
  • village
  • it takes a village
  • teach a man to fish
  • a little knowledge is a dangerous thing
  • a little learning is a dangerous thing
  • the best-laid plans of mice and men