When I was a child about seven years of age, my friends one holiday filled my pockets with half-pence. I went directly to a shop where toys were sold for children, and being charmed with the sound of a whistle that I saw on my way in the hands of another boy, I voluntarily offered him all my money for it. I then came home, and went whistling over the house, much pleased with my whistle, but disturbing all the family. My brothers and sisters and cousins, understanding the bargain which I had made, told me that I had given four times as much for it as it was worth. This put me in mind of what good things I might have bought with the rest of the money, and they laughed at me so much for my folly that I cried with vexation. My reflections on the subject gave me more chagrin than the whistle gave me pleasure.

This little event, however, was afterwards of great use to me, the impression continuing on my mind, so that often, when I was tempted to buy some unnecessary thing, I said to myself, 'Do not give too much for the whistle,' and so I saved my money.

From 'Benjamin Franklin's Life.'