The market -- any market -- is a system for telling us how much things cost and whether we can afford them. If we use cash, a glance in our wallets tells us how much we can buy -- loud and clear.
With plastic you get an ambiguous answer for a long time, but eventually the Plastic Lawyers come around and take your stuff. Then you know.
It was McGee's buddy Meyer who said: "Everything is easier when you face reality."