"A group of people (in this case about 150 young couples with congressional connections) agrees to baby-sit for one another, obviating the need for cash payments to adolescents. It's a mutually beneficial arrangement: A couple that already has children around may find that watching another couple's kids for an evening is not that much of an additional burden, certainly compared with the benefit of receiving the same service some other evening. But there must be a system for making sure each couple does its fair share.
The Capitol Hill co-op adopted one fairly natural solution. It issued scrip—pieces of paper equivalent to one hour of baby-sitting time. Baby sitters would receive the appropriate number of coupons directly from the baby sittees. This made the system self-enforcing: Over time, each couple would automatically do as much baby-sitting as it received in return. As long as the people were reliable—and these young professionals certainly were—what could go wrong?
Well, it turned out that there was a small technical problem. Think about the coupon holdings of a typical couple. During periods when it had few occasions to go out, a couple would probably try to build up a reserve—then run that reserve down when the occasions arose. There would be an averaging out of these demands. One couple would be going out when another was staying at home. But since many couples would be holding reserves of coupons at any given time, the co-op needed to have a fairly large amount of scrip in circulation.
Now what happened in the Sweeneys' co-op was that, for complicated reasons involving the collection and use of dues (paid in scrip), the number of coupons in circulation became quite low. As a result, most couples were anxious to add to their reserves by baby-sitting, reluctant to run them down by going out. But one couple's decision to go out was another's chance to baby-sit; so it became difficult to earn coupons. Knowing this, couples became even more reluctant to use their reserves except on special occasions, reducing baby-sitting opportunities still further.
In short, the co-op had fallen into a recession.
Since most of the co-op's members were lawyers, it was difficult to convince them the problem was monetary. They tried to legislate recovery—passing a rule requiring each couple to go out at least twice a month. But eventually the economists prevailed. More coupons were issued, couples became more willing to go out, opportunities to baby-sit multiplied, and everyone was happy. Eventually, of course, the co-op issued too much scrip, leading to different problems ...
If you think this is a silly story, a waste of your time, shame on you."