Professor Herbener, I’m afraid your answer made me a bit confused. When will an actor ever be in a state that compels him to give up the 8th unit of D in order to get a 5th unit of A? If he ranks his ends and chooses accordingly then he will always be satisfied with choosing D over A (ex ante, and given the current configuration of his values and his supply), since the 8th unit of D is higher on his scale of preference than the 5th unit of A? If the differences between the MU were substantial he would still choose in the same way, wouldn’t he? The differences between the MU of the goods seem irrelevant. What am I missing?