YOU CAN’T HAVE CAKE AND THE TOPPING, TOO
(USA) This idiom means that you can’t have everything the way you want it, especially if your desires are contradictory.
YOU CAN’T HAVE YOUR CAKE AND EAT IT
This idiom means that you can’t have things both ways. For example, you can’t have very low taxes and a high standard of state care.
YOU CAN’T MAKE A SILK PURSE OUT OF A SOW’S EAR
If something isn’t very good to start with, you can’t do much to improve it.