I think it also serves to illustrate that there are things that can be paid for that don't increase quality of life. Likewise, if person A and B buy from each

I think it also serves to illustrate that there are things that can be paid for that don't increase quality of life. Likewise, if person A and B buy from each other at the same monetary value, but the subjective value of what they "traded" is valued more by the other party, then each party is wealthier despite no change in pure monetary wealth.