Charlie feels I did not explain things well in my last post. He feels I ought to try again. So I am.

I want to imagine you are choosing one of those tubs of ice cream with a good friend. You must, temporarily, pretend that there are no small containers of ice cream available. You cannot get two single servings that are different. There are only the large sizes suitable for a family, and you must agree on the variety. You must also pretend with me that you and your friend each have favourite ice cream flavours that the other hates.

The decision-making tree will go differently for this scenario depending on whether you are collective or two individuals, and the best choice of action will probably be different also. There are still two basic choices about how to go about this, but they will look very different depending on…