You can get from people only what they are able or willing to give; trying to do an impossible tas

I agree that it's a low-quality result, but the worker did the best that he could with the very few and inadequate resources at his disposal. After all, there's no getting blood from a stone

Ne convengo che il lavoro è mediocre, ma l'operaio ha fatto del suo meglio con lo scarsissimo materiale a disposizione e non si può certo pretendere che cavi sangue da un sasso

You cannot, obviously, extract something that is not there to begin with. The Roman playwright Plautus (254-184 B.C.) wrote in his comedy Persa (I.i.42): “nam tu aquam a pumice nunc postulas” (you cannot wring water out of a pumice)