beggars cant be choosers

Beggars cant be choosers is a cliche often used to refer to the fact that when you receive something you have been asking for, you should not complain about what you are given. It is a phrase often used when someone begs for something over and over again, quite vocally and publicly, but then when they receive what they begged for, it is not what they imagined it to be or not as much as they wanted (such as monetary value) and then complain about it.