When I was a child of seven years old, my friends, on a holiday, filled my pocket with coppers. I went directly to a shop where they sold toys for children; and, being charmed with the sound of a whistle, that I met by the way in the hands of another boy, I voluntarily offered and gave all my money for one. I then came home, and went whistling all over the house, much pleased with my whistle, but disturbing all the family. My brothers, and sisters, and cousins, understanding the bargain I had made, told me I had given four times as much for it as it was worth; put me in mind what good things I might have bought with the rest of the money; and laughed at me so much for my folly, that I cried with vexation; and the reflection gave me more chagrin than the whistle gave me pleasure. This however was afterwards of 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, "Don't give too much for the whistle;" and I saved my money.
Source: letter to Madame Brillon, Nov 10, 1779. —The Works of Benjamin Franklin, ed. J Sparks,1836
Contributed by: Zaady