People who can not choose what they will have, must accept what they get; if you are not in control, you must take what you can gel. We wanted to leave on the train in the morning but it doesn't go until afternoon, so we must go then. Beggars can't he choosers. Mary got a red dress from her sister, although she didn't like red. She kept it because she said beggars should not be choosers.
Compare: LOOK A GIFT HORSE IN THE MOUTH.