In individual self-centered values, there may not be uniformity of intensity with which a thing is desired. Even a universal article, standardized like money, will not necessarily represent quality in satisfaction.
A rupee in the hands of a farmer may represent one day's food for his family. The same rupee, with a clerk in a city, maybe the satisfaction of seeing a cinema. While in the hands of the rich, a mere tip to a waiter. Hence, the transfer of a rupee from a rich man to a farmer will enhance the capability of affording, but a rupee taken from a farmer and passed onto a rich man reduces the satisfaction.
As an example, a boy may have 7 jalebis. Each jalebi may be equal in weight and content, yet the satisfaction one jalebi will bring will not be the same as another. He will eat the first jalebi with much relish. The next one or two he will still enjoy. Then with each individual jalebis eaten, the desire for more will diminish until it reaches a point where it will be nauseating to think of having anymore. So the value of the jalebi to the boy goes on decreasing as the number consumed increases.
Now, when a boy has eaten, say 6 jalebis and his desire for more has decreased while the thirst for the water has increased, he would gladly swap the 7th jalebi for a glass of water with another boy who may have a pot-full of it. The glass of water will represent greater satisfaction to him than the 7th jalebi, while to the second boy that jalebi, which is first to him and 7th to the other, will bring much relish. The exchange of goods - the 7th jalebi for a glass of water - bring more satisfaction, and if we can measure the happiness of the two boys before and after the transaction, we shall find that though the sum total of goods with the boys remain the same, yet the aggregate happiness after the exchange is much greater than before it.
This is the basis of all trade. Both the buyer and the seller gain mutually. Nobody's loss should be another's gain.
As told by J.C.Kumarappa.