It just means a person wants everything pertaining to the subject it's being said about. They don't seem to be satisfied with just a part.
"It can be used to say that one cannot or should not have or want more than one deserves or is reasonable, or that one cannot or should not try to have two incompatible things. The proverb's meaning is similar to the phrases "you can't have it both ways" and "you can't have the best of both worlds.""
Preachers who say "hello?" while they preach and want an Amen.
Or, "Come on!" to get people to engage.
Our assistant pastor/woriship leader says it so much, some people will actually count how many times he says it in a worship session. (thirty-some, I've heard)
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