L'erba voglio non cresce neanche nel giardino del re: The grass of 'I want' does not grow even in the garden of the king.
My friend told me this Italian proverb the other day. I'm not really sure how to translate it properly, but he said that this is what Italian parents tell their children when they use 'I want' too much; not even kings get everything they want. It sounds so much prettier in Italian.