You can’t take it with you
You can’t make an omelet without breaking eggs.
You can catch more flies with honey than with vinegar.
You can’t teach an old dog new tricks.
You can’t always get what you want.
Your Guess Is as Good as Mine
You can’t fit a round peg in a square hole.
You can say that again
Your guess is as good as mine
You can’t unscramble a scrambled egg.