How we change what others think, feel, believe and do
Penny and Bun
Highlight a contradiction within the proposal where it seems they are suggesting two mutually exclusive things are both possible, such that you will get the 'penny and the bun'.
Show that this is a choice between alternatives, not a 'you can have it all' option. Then argue about which choice will be most appropriate, maybe suggesting that further consultation would be needed.
You can't have the penny and the bun. You are suggesting we can cut costs whilst also increasing sales. That's nonsense.
We've only got limited budget for this. We can't afford all three. We'll have to choose one, which means I'll have to ballot my members.
You want to take everything I have yet also stay my friend. Sorry, but you can't have it both ways.
Having the 'penny and the bun' means having two things which cannot be had together. If you are buying a bun that costs a penny, it is an exchange and you cannot have both.
A similar saying is that 'you cannot have your cake and eat it'.
Sometimes people promise more than is practically feasible in order to get your agreement today. By recognizing this you can use the saying about the penny and the bun or otherwise show that you know that what is being proposed is infeasible.
Sometimes it is possible to have more than is being offered and the other side may use the 'penny and the bun' argument. If you have power, for example when they need agreement more than you, then you can demand more.